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Full text of "Practical Television 1969 April"

PRACTICAL 



3D 



APRIL 
1969 




also inside 



UNDERSTANDING COLOUR FAULTS 





BENTLEY ACOUSTIC 




RBF89 

EBL21 


B 3 
11 
48 


i-'l * . 

ef«>; 


9,6 
6,8 
6- 


HAHiSliS' 
HL2 7 6 
BtlJC 4,- 


. 


87 8 

10 6 


FY 11 

4." 10 


69 
56 
8- 




CORPORATION LTD. 




15C34 

m."o 


12,8 
8.- 
4 9 


EFSU 

El 01 
EF22 


49 
33 
2 6 


HL22 10. 8 
UJ.41DP 


PCFS4 8- 
PCFS6 8; - 
FCF801 7l- 


QSlW/lfi 

96 


1 12 14 

l/Ti 
I 17 


70 
15,- 
S, 








BC86 


10; 3 


KI-'*.'7 


10,- 


19/8 


PCF88S 9,- 


f!iu 15/- 


L'lM/20 10/ 




3SCHALCOT ROAD, CHALK FARM, LONDON, N.W.1 




EC88 


10/3 


Blf96 


10,6 


11L 12111)8/ 




Kll 19/6 


U19 


::■'>■ 








ECSW 


«.'« 


EF183 


6;- 


ERfSOJ 27 ■! 




RIG 84/11 


B50 


7/0 




THE VALVE SPECIALISTS Telephone PRIMROSE «M 




HOC31 


15 8 


EF184 


8 


H\'H2 89 




El< 17 6 


i. 29 


13 








BO S3 


46 


EE90 


6/6 


HVR'M 8/9 


pclsi »;- 


B18 8/6 


oa 


116 




SAME DAY DESPATCH BY FIRST CLASS MAIL 




BOOH 
SOCM 

ECC40 


29.1 
296 
98 


EE3-2 

EL33 
EL34 


86 

12- 
96 


IW3 5 8 


PCE82 7/- 
PCLS3 9/- 
PCE34 7/8 


K1L' 6 6 
BS2 7/6 
KK34 76 


0S1 
U33 
U35 


6 
29 8 
16 6 


OA2 


ft 


tJARrt 80- 


BL7GI 12 a 


10P14 12 6 


2SZ4G e;- 


305 186 


Hil'V 


4/- 


OB'i 


6 ■ 


8AT6 ii- 




1-2 A' - , 8/8 


28ZB 7/- 


306 18/- 


DHS1 


10,9 


ECX381 


39 


EE35 


lo- 




PCE85 8,'8 




L'37 


34 11 


OZ4 


4.3 


SA1 '. 6 - 


RL1U 19; • 


12AC0 7/- 


waa 8 6 


807 11/9 


DK32 


71- 
10- 


1 


4 8 


EE36 


se 


Era u/t 


PCLS6 8/8 


rti'01 3/3 


F45 


15 a 


LAS 


«/8 


tJAVti 676 


fiLD'iG Sil 


12AD6 6/- 


90C1 6/6 


958 87- 


BH40 


BCC83 


4/6 


RL37 


17 3 


ki..i, ii i 


PCX88 16/- 


THTJ4 83 


t:ao 


5 8 


I At 


&/- 




6H70T 6'6 


12AE6 7/6 


30C15 13/8 


1821 10/8 


DK91 


6/6 

7/8 


EO084 


6/8 


EL41 


9/3 


KLL32 21/7 


PEK45 7/- 


TH4B 10/- 


U32 


■! 11 


1A70T 


1>- 


8 H l-M. 4.3 


BP1 12/- 


12ATA 4/8 


mil"!- 18.8 


5763 10/- 


DK92 


ECC85 


B- 


HL43 


9/9 


KT2 5,'- 


PEX45«U 




U76 


4/B 


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12AT7 3/9 


HOiUs S-9 


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1JK96 


11- 
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46 


80068 


7 


ELS1 


8/- 


Ki'- 14/8 


12 




L - 78 


11 II 


1D5 


6/9 


iilUii 8/9 


rll'i'l IK 


12AU6 4/9 


30FS 13/6 


7475 */- 


IU,33 


ECC1S8 


98 


EL83 


6/6 


KT82 5/6 


PKS4S 4 


i ABO80 59 


F107 


IS. 3 


1D(J 


98 


S11Q3 4.(6 


riPi* 25; 


12AU7 4)8 


MP] i 15- 


A1334 20/- 


lil.:;,' 


ECCS07B7- 


EL84 


46 


KT41 196 


PEN 38 S 9/6 




V1H1 


12/8 


LFin 


8 - 


UBQ7A 7/- 


gq;« 6/- 


12AV6 58 


91 US 16- 


A2134 10'- 


DtSi 


4/6 


F.f.:F-" 


6 8 


EL85 


76 


KT44 20- 




VB41 6/8 


man 


16 


1FM 


3 9 


6BB7 88 


8Q70T 8/6 


12AX7 4 6 


SOFLU 12,8 


A864S til 


DIM 


5/6 




66 


UL88 


8 


KT81 12/- 


116 


I Kf41 7 6 




B- 




6 


6 11 if 6 8- 


SR7(. 7 


12AY7 9 9 


;«Li 8 : - 


AC2PEX 


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11- 


ECFSfi 


8 


EL91 


2/6 


kt.jo i - 




•L'BC^l 7''- 


caua 


8 - 


1H3GT 


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6B87 166 


B8A7QT 5 - 


12BA6 8;- 


30L15 13/9 


16.6 


1>M70 


8 - 


■d 




EESo 


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KT66 17,8 


19 6 


DBP80 5 9 


tt301 


11 


1X4 


88 


nawa jj>.9 


• 


12B£6 5 9 


S0L17 18/- 


A.C2PEN; 


DM71 


7/6 




42 


E.W71 


14/- 


KT71 12,6 


PF._N"A4 19 8 


(.'BF89 6/9 




16 


u.m 


V- 


'■-BWT 11/- 


6907 87- 


12E1 17/- 


30P4 18/- 


DD 19/8 


DW4/3i»u 


ECH21 


126 


BS86 


59 


B 


PENiDD " 


1 HL21 9- 




6 6 




8'- 


K i 2/9 


83H7 3,'- 


I'iJTOT 8 6 


3DP-1MR 


AC6PEN4/9 




8/B 


BCHSS 22 8 


L11S1 


69 


KT88 29.- 


; :■' . ■ ii 


UU92 S/6 




76 


IK SOT 


7.9 


<1CS 8/9 


89J 1 8 6 


12KS 10/- 


17/8 


AC/PBH (5) 


IJWl;5uu 


ECH35 


5/9 


BH84 


6/- 


strwei s a 


PFL2001B- 


l'CC84 8/- 


UB01 


18- 


1E5 


m 


6C9 11/- 


8SK7 4/6 


12K7C.T 5;B 


S0P12 18/- 


19/8 




8/6 


ECU vi 


10/- 


EM So 


11/- 


KTW6210J 


FL33 19 6 




VP4A 


14'6 


184 


*<» 


«CD6G 19/6 


8SX7GT 4/6 


12KSGT 7'8 


30P19 lit- 


AC/PEN (7) 


DYS8 


8/9 


BCH81 


5/9 


EMS7 


73 


KTW83 5/6 


KM 1 ii 


PCF86 8/3 


VTili 


10'8 


1S5 


a/» 


BCBfl 6.- 


fi8Q7GT 8/- 


12Q7GT 4/6 


3HPL1 16/- 


19,6 


DY87 


6/9 


ECH83 


8/- 


EV01 


89 


KTZI1 6- 


Pl«l 7/8 


OCHB1 8/- 


^T13C 


7 


1U4 


5 9 


(0W4 13- 


BtriGT IE/-- 


12SA7GT 


3HPL13 16/- 


AC/TH1 


nop 


24/- 


ECH81 


7 


EY?1 


7 - 


L63 8/9 


PL81A 10 6 


OCB49 9/9 


\T>23 


28 


1C5 


69 


6D3 7/6 


fiuaa 6/- 


89 


S0FL14 16/- 


10/~ 


■88P 


84- 


EC LSU 


66 


BY8S 


S3 


LP2 9 8 


FL82 6 6 


UCU81 6/6 


VK78 


24 


•2JJ21 


66 


8Dfl 3 - 


6U7G 7/- 


l*iS'VT 4 - 


30rL15 15/- 


AC/TP 19/8 


B88O0 


12 


ECL82 


6 


BYS4 


7 8 


M DM 8 3 


PL83 6,8 


■ 


YE 105 


5- 


IA4 


36 


flFl 8 9 


avsr. 3/6 


12SG7 3'- 


33 A5 15- 


AC/YP210;6 


K180P 


17 6 


ECL83 


8/- 


BYSfl 


6- 


>IHl.l»i 7 8 


PL84 6 3 




YK150 


6- 


3A3 


10 




BYflGT 67- 


12SH7 8;- 


S5L6GT S 


ATIM 2/3 


E114S 


10 6 


ECL84 


12- 


EY87 


8- 


MLti a - 


PL ■;•.!» 12 


IF41 9 8 


VT61A 


7/- 


3B7 


5- 


•Ti-J 8/3 


3X4 3.8 


12SJ7 4/8 


35 W4 4/6 


AZ1 8 


EAaO 


18 


ECL85 11/- 


EY88 


78 


ill 13/144 - 


PttM J2h 


LF42 8/- 


VU111 


7,3 


3DB 


39 


OF J 3 8/8 


txacn & 


ISSK7 4,9 


ariZ.i io- 


AZ31 8/9 


F.A76 


13- 


Kl i.«: 


8/- 


EVHl 


3 - 


MX 40 12; B 


rUH 2.H St 


l - F80 6/B 


; L i^" 


12 


3Q4 


6/6 


'It'll 15- 


SY7U 1B/B 


128Q7GT7/8 


862401 4'B 


A241 7/6 


EA BC80 8.- 


ECLL800 


EZ35 


6/- 


N7B 88/4 


PI>802 16/- 


I 1 FSB 6/9 


\TI2UA12- 


3Q5GT 


«/ 


KPU 9/a 


::■■:• inft 


12 Sit 7 &,- 


S6Z6UT 8- 


BL63 10/-- 


EACitl 


8/- 




:». 


E7Aft 


7;3 


NS39 25/- 


FM84 7;9 


UF88 9/- 


VU1S8 


7 


334 


4/8 


::: ' 


7B7 7/- 


12Y4 B/- 


0I1A5 21/10 


c:L33 18/6 


EAF42 


8/B 


EF22 


12 li 


EZ41 


7/3 


P81 2/8 


PT89 98 


UF3B 6/3 


W61M 


24/8 


av-1 


S.e 


I1F1S 7/6 


Vfli 61 


UH7 9/8 


50R3 6/8 


eve lo/e 


1-. n:;t 


7/6 


i:!">: 


3/6 


EZ80 


4/3 


FAHl'fO 7; 3 


PYS3 fl/6 


UL41 9/6 


TV7fi 


59 


6R4OY 


89 


1 :■: a I 


7H7 6'8 


14S7 15/- 


noa va 


CY1C 10/6 


EB41 


4/6 


LI 'BY A 


7/- 


Ezei 


4.8 


POM 9.6 


FY80 6/8 


1LHS 12/6 


W107 


7/- 


BU4U 


4 9 


131*44 11/9 


7B7 12- 


13 12 6 


., ■!..,.. 41 . 


CY31 7/8 


! R'l] 


2 3 


EF3B 


5 


Br£M 


3 6 


PC88 9/8 


PV81 5 3 


FLH4 6/6 


W728 


10- 




78 


«F28 10/6 


7S7 80'- 


1'J 10 '6 


SOI-OGT 6/- 


PBS S/- 


i BOS 


26.6 


RF46 


8 9 


F1V4 51106,8 




PYfiS 5- 


MM 5- 


Y41 


10- 




56 


fiFS'2 8/- 


7V7 6/- 


1«A(J5 4 9 


n 6;6 


D77 2/8 


BBOO 


S'8 


F.F4 1 


96 


FW"4;S0fl 


P081 8. 6 


PY8S 56 


IK1C 10.8 


X61 


69 


5Z-J 


8 


0O6G s/e 


7Y4 8/6 


2MH 18/- 


S5A2 8 6 


DAC32 7/- 


! BC81 


5 e 


EF42 


1 6 




10 


PCSWO 8/3 


PY88 6:3 


rue ii- 


X65 


5< 


. 


8 9 


lilliifiT 19 


9BVV6 Jf 


20i>4 20,5 


B0A< t<7 e 


BAP91 8/9 


| B> ■• 1 


*/- 


EFBO 


2 6 


B089 


9 '- 


l'i ■ -i |r- 


FY800 6 6 


i 1 i 14- 


Xtih 


7'6 




12 6 


81 SO 3/9 


9D7 %h 


20F2 14,'- 


'JOAV 67/8 


DAP9A 6/- 


BB091 


6/6 


EF54 


10 


GZ38 


12,6 


PCC85 8/6 


FY S01 6 6 


I t 12 4/6 


X81M 


■M li 




5 6 


Ufl 3 - 


lOUl 12 6 


2(JL1 13,- 


WOO 34;- 


DCC90 10,- 


KBI'SO 


6 - 


EF73 


UK 


ozai 


10/- 


• 


Ql-21 S 


im« 9. - 


YU3 


5 


■ 
IA07 


3 

6/9 


6J7G 4,9 

0,170 T 8/6 


IflCS 10- 

lulil 8' 


20P1 17/8 
■20P3 18/- 


80OT 88/8 

mm 18 


DD4 10/6 
DDT4 8'3 


EBF83 


8 - 


BF80 


1 8 


UZ37 


14/6 


POC89 H 


QYQQ3, Id 


DTffl 9 6 


Z399 


13 u 

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All j?i,odB fire ntiw, lltHt 


Quality BUum&etiEpe only, and kubje^t fco maker*! full num'iLntee. W^ t 


■ 


4 8 


SKSGX 5 


Jrtl'W 14 7 


2ffP4 18/6 


1S0BS 14 6 


DF33 7/9 


hawk 


maiiufa^UiriT* 


' neotmdB nor rejects, which an niter deaaribod u "new and bestad" 


IJAKli 


it 


JK70 £-- 


10F1 15- 


SOPS 18 


i ■' 5 S 


BBS i 1 9 


but have a limited and unjj-.ii;yhle life. 'Bodotm bom* Mf.n.-Fii Hjl 1-,'n Satfi. 9-1 p.in. 


SALS 


9 3 


I 


10F9 9;- 


25ASQ 7/8 


KWJBT 35,- 


PF96 8,'- 


T«rmfl of busineeg. C»«h with order iiul\. l'.-t 'lui.-klns Ud m li.-m Orfers nrm £S ui«l," 




16 6 


I 


lOFta 7,6 


23LSGT 5/6 


80] 20/- 


BP97 10/ - 


pacting free. All owiern olrared on 


day ot nestDt. Anv parcel insured aealnM daoiaec in transit 


.-. .:■■ 


3 3 


KL1 19 8 


10LU1I 10- 


25Y6 6/- 


302 16/6 


DH63 6/- 


ha only 6d. eitra, Cotnplrle eatjilosne ol viilvp.». Lranslsttjrs and cnmuimpuli with ooudltl' 


- , . : 


■ MJS 


4 9 liLvGT 7.9"10P1M 13 **WBB 8.6 303 IB- DH78 4.0 Kile, price lOd. post Ik,' 


[tfrke enewerrd iinLe«£ a.A_E. HUd m d for reply. 





T.V. 
TUBES 



"VIDE0CHR0ME" 

FOR BRILLIANCE & DEFINITION 



T.V. 

TUBES 




COMPARE 
OUR 
PRICES 
17* — £4-15-0 
19*— £5-5-0 
2r_£6-IO-0 
23 w — £7-10-0 

TRADE SUPPLIED 
ALL TUBES PRECISION REBUILT AT OUR 
OWN FACTORY BY SKILLED CRAFTSMEN 
WHO HAVE BEEN REBUILDING TUBES 
FOR OVER 10 YEARS # EACH TUBE 
BENCH AND SET TESTED TO A VERY 
HIGH STANDARD BEFORE DISPATCH 

PRICES FOR TWIN PANEL TUBES 

AVAILABLE ON REQUEST 

2 YEARS GUARANTEE FREE 
DELIVERY ANYWHERE IN THE U.K. 

VIDEOCHROME TUBES LTD. 

25 BELLEVUE AVENUE, 

RAMSGATE, KENT, Tel. THANET 52914 



17in. — £11.10.0 
19in. SLIMLINE 
SOBELL— 24 Gns. 



TWO-YEAR GUARANTEE 
EX-RENTAL TELEVISIONS 



FREE ILLUSTRATED 

LIST OF TELEVISIONS 

17"— 19"— 21"— 23* 

WIDE RANGE OF MODELS 

SIZES AND PRICES 

DEMONSTRATIONS DAILY 



TWO-YEAR GUARANTEED 
TUBES 100 . REGUNNED 
Slim Line Tube* NO" 17" and 19" 99 6. 
21 "and 23* 119 6. 

Normal lubes 70* and 90° 17" 89/6. 
2t" 109,6. 14" and other sizes 69 6. 




COCKTAIL STEREOGRAM CABINET £25 

Polished walnut veneer with 
elegant glass fronted cocktail 
compartment, padded. Petition 
for two lOin. elliptical speakers. 
Record storage space. Height 
35±in.. width S2fin„ depth I44>. 
Legs I gn, extra. 

Speakers 6 6: 2"— 750. 1Y'~ 35 
n. P. & P. 2/6. Aeos Mies. *5> 
iHH Standard; Stick Mic, 2gns. P. St 
P J/6, A»tld. Condensers; 10/. 
for 50. P. & P. 7/6. As»td. 
Resistors I 107- for 50. P. & P. 
4.6, Asstd. Controls: 10 - for 
25. P. & P. 7/6. Transistors: 
Mullard matched output k,t 9^ 

oca id— 2 ocei-s, p. & p, free, 

Ferrite Rods 3,'6t 6" x J" complete with LW.MW Coils. P. & P, FREE. 

TRANSISTOR CASES 19 6. Cloth covered, many colours Size 9," x 6i" 

x 3|" P. Si P, -4,6. Similar cases in plastic 7/6. 

TRANSISTOR RECORD PLAYER CABINETS 19 6. Dim I I" x I4>" x 

Si". P. & P. 7/6. 

SINGLE PLAYER CABINETS 19,6. P. & P. 7 6. 

STRIP LIGHT TUBES 39 each. I t"(2e4 mm.) 230/240 volts. 30 watts. Ideal 

for cocktail cabinets, illuminating pictures, diffused lighting etc, 6 for £1. 

P. & P. free. 

DUKE & CO. (LONDON) LTD. 

621,3 Romford Road, London. EI2 Tel. 01-478 6001 2' 3 




289 



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IKS 


4/e 


EOCSffl 


6/6 


FCL83 


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195 


4/S 


ECH35 


8/8 


PCL84 


11- 


1T4 


2/B 


ECH42 


10/8 


PCL8B 


8/9 


394 


6/9 


ECH81 


6/9 


PCL8B 


8/8 


3V4 


5/8 


ECLflO 


7/8 


PFL200 


w- 


8AQ5 


4/6 


KfLH'2 


6/3 


PL36 


9/e 


8L1S 


■/- 


ECL83 


8/9 


PL81 


7/- 


30C18 


3/9 


ECL8S 


7/8 


PL82 


S/9 


SMU 


18/6 


EF39 


8/fl 


PL83 


6/S 


30FLI2 


14/3 


EF38 


4/9 


PL84 


6/3 


S0FL14 


10/3 


izvm 


6/- 


PLSOO 


13/9 


30P4 


11/6 


EF88 


8/3 


PLS04 


13/3 


30P1A 


11/6 


EF89 


4/9 


PY32 


10/- 


30PL1 


ie/s 


El-'IK! 


5/9 


PY33 


1(1/- 


30FI.13 


14/3 


GF1S4 


5/6 


PY81 


s/- 


CCH35 


s/e 


EL33 


8/3 


PY82 


5/- 


CL33 


17/6 


EL41 


10/3 


PY83 


5/3 


DAC32 


6/S 


ELS4 


4/6 


PY88 


6/- 


DAFS1 


4/3 


EYB1 


7/8 


PY800 


7/3 


DAF96 


6/3 


KV«*1 


8/6 


FY801 


6/8 


DF33 


7/fl 


BZ80 


s/e 


Slfi 


8/3 


DF91 


2 8 


EZS1 


4/6 


D2B 


18/9 


DF96 


6/U 


KT81 


8/3 


U2B 


11/6 


DK32 


6/9 


KT8B 


15/9 


Ulfll 


12/3 


DK91 


4/9 


NTS 


14/6 


UABC80 


S/S 


DE96 


6/6 


PABC80 


6/9 


UBC41 


8/3 


DL36 


4/9 


evtt 


10 3 


UBF89 


6/S 


DL93 


m 


PC88 


10/3 


UCC84 


7/9 


DL94 


5,8 


PC97 


7/9 


UCC85 


91- 


DL96 


6/9 


PC900 


8/- 


UCF80 


B/- 


DT86 


6/S 


POC84 


S/S 


UCH42 


9/8 


DY87 


5.8 


PCC8B 


9/9 


UCH81 


6/S 


EABC60 


6/9 


rn-isn 


9/6 


UCL82 


6/S 


EBC41 


8/~ 


PCF80 


6/8 


UF41 


9/8 


EBF80 


6/- 


PCF82 


5/9 


UFSfl 


6/6 


EBF89 


6/S 


PCF801 


6/9 


UE41 


10/8 


ECC81 


3/9 


POT8W 


8/8 


UtB4 


6/9 


Bocea 


4; a 


PUF808 


10/3 


UY41 


8/8 


EOC83 


4/6 


PCL82 


6,9 


UY86 


5/8 


Postage on 


1 valvr. 


9d. extra 


On a 


valves or 


more, 


postage Bd, 


per vali 


re extra, • 


Lny pare 


el Insured against 




dam 


age In transit Bd. e 


Etra. 






Offl 


e address, 


1:1 callc 


s. 





GERALD BERNARD 

83 OSBALDESTON ROAD 

STOKE NEWINGTON 

LONDON, N.16 



BRAND NEW LINE OUTPUT TRANSFORMERS 

ALBA 655, 565, 77/6. 

DYNATRON TV30, TV35 48/6, TV36 70/-. 

EKCO T231 , T284, TC267, T283, T293, T31 1 , T326, T327, T330 48/6. TM B272 68/6. T344 

T344F, T345, TP347, T348, T348F, TC347, TC349, TC356, T368, T370, TC369 T371 

T372, TP373, TC374, T377A, T380, T380F, T381 , T382, TC386, T393, T394, all at 70/- 
FERGUSON 306T, 308T 48/6 each. 406T, 408T, 416, 436, 438, 506, 506, 516 516 

536, 546, 604, 606, 608, 616, 619, 636, 646, 648, 725, 726, 727, 3600, 3601 3602' 

3604, 3611, 3612, 3614, 3617, 3618, 3619, 3620, 3621, 3622, 3623, 3624, 3625' 

3626, 3627, 3629 65/-. 
FERRANTI T1001, T1002, T1 002/1, T1004, T1005 48/6. T1023, T1024, T1027, T1027F 

TP1026, T1057, T1057F, T1058, T1061, T1063, T1063F, T1068, T1068F T1071 

T1072 70/-. 
G.E.C. BT302, BT304 62/6. 

H.M.V. 1865, 1869 48/6. 1870, 1872, 1874, 1876, 1890, 1892, 1894, 1896 65/- 
PILOT PT450, 452, 455, 650, PT651, P60A, P61 82/6. 
PHILCO 1962, 1967, 1967M, 1019, 1020, 2021 82/6. 1029, 1030, 1035, 1036, 1040 

1 050, 1 060 82/6. 
PYE V200, V400, 200LB, 210, 220, 300F, 300S, 31 0, 21 OS, 41 60/-. 

Please state part No, 
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LINE OUTPUT TRANSFORMER INSERTS 
BUSH TV53, TV56, T57, TV57, TUG 58, M59, TUG 59, TV62, TV63, TV66, TV67 TUG 68 

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EMERSON E700, E701, E704, E707, E708, E709, E710, E711, Portarama 32/6. 
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FERRANTI 14T2, 14TC, 14T3F, 14T4, 14T4F, 14T5, 14T6, 17K3, 17K3F, 17T3, 17T3F, 

1 7K4F, 1 7K6, 1 7SK6, 1 7T4, 1 7T4F, 1 7T5, 1 7T6, J1 K6, 21 K6V 32/6. 
1NVICTA T1 1 8, T1 1 9, T1 20 40/-. 

K.B. PV40, MV100, OF100, PV100, NV40, NF70, OV30, QV10, QV30 32/6 pair. 
PETO SCOTT 1416, 1418, 1419, 1422, 1423, 1716, 1719, 1720, 1922, 1723, 1724, 

1 725 29/6. 
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Guarantee. Post and Package 4(6. C. O.D. €/-. 

All new components inserts are guaranteed for three months from the date of invoice 
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D. & B. TELEVISION (Wimbledon) LTD 

80 MERTON HIGH STREET, S.W.I 9 
01 -540 3513 01 -540 3955 



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PRACTICAL 

TELEUISIOn 



VOL 19 No 7 
ISSUE 223 

APRIL 1969 



What Substitute? 

IF WE were commercial TV advertising 
copywriters this would be the opportunity 
of a lifetime. Imagine the possibilities — 
"This is it, folks, the BIG onel" . . , "Practical 
Television now comes to you in the large 
economy size pack" , . , "PT uses paper 
whiter than white" . . . "Get the strength of 
our Query Service around you" . . . 

There is, however, one that we'd like to 
borrow in all seriousness and that is "You 
know that Practical Television makes sense" I 
With the larger page size, more attractive 
layouts will be possible and articles will be 
easier to read, as will some of the larger 
circuit diagrams. 

PT has held a unique position in the 
technical publication field since the bold 
move to launch it in the early 1930s. Since 
then, despite a few rough passages due to 
prevailing circumstances (mainly a World 
War), it has reflected and commented on all 
the major technical trends through the years. 
It was as up-to-date in 1934 with its con- 
structional articles on scanning discs as it is 
today with the latest and authoritative 
articles on colour television. In beginning 
this new chapter in the life of PT we make one 
concession to our convictions. From here on 
we abandon c/s and kc/s etc. for Hz, kHz; 
we disagree with the change as a change, 
but the whole of industry has now swung 
over, as have nearly all other periodicals 
(some, like us, simply to avoid rocking the 
boat). 

Finally, to return to the dreamworld of the 
"commercials," it would be appropriate to 
borrow another famous old cliche: "Look 
for the genuine label — Accept No Sub- 
stitutes," What an idea! There is no sub- 
stitute for PT; it is still the only magazine 
you can buy on the bookstalls which is 
devoted almost exclusively to the technical 
aspects of television! 

W. N. STEVENS, Editor, 



THIS MONTH 

Teletopics 



Letters to the Editor 



292 



Installing and Servicing Colour Re- 
ceivers — Part 7 — Understanding 
Colour Faults 

by P. G. Alfred 294 

Apollo 8 TV Pictures 

Richard Collins reports 298 

Servicing Television Receivers — 
Thorn 950/960 chassis 

by L Lawry-Johns 301 



304 



Valve and Component Overheating — 
Part 2 by G. R. W tiding 306 

Practical Aerial Design — Part 2 

by A. J. Whittaker 309 

The PTV Videoscope MV3 

by Martin L Michaelis, M.A, 312 

Television Receiver Testing — Part 10 
— Flywheel Sync Circuits 

by Gordon J. King 319 

DX-TV by Charles Rafarel 323 

Service Notebook by G. R. Wilding 324 

Underneath the Dipole by Iconos 326 

Your Problems Solved 329 

Test Case 77 331 

THE NEXT ISSUE DATED MAY WILL BE 
PUBLISHED APRIL 18 



All correspondence intended for the Editor should be addressed to: The Editor, "Practical Television", IPC Magazines Ltd., Tower House, Southampton 
Street, London, WC2. © IPC Magazines Ltd., 1 969. Copyright in all drawings, photographs and articles published in "Practical Television" is 
specifically reserved throughout the countries signatory to the Berne Convention and the USA. Reproduction or imitation of any of these is therefore 
expressly forbidden. 



292 




PAL COLOUR TV TEST SIGNAL GENERATOR 




Type 141 PAL TV test signal generator marketed by Tektronix UK Ltd., 
Beaverton House, Station Approach, Harpenden, Herts, provides high- 
quality TV test signals for 625-line 50Hz field standard PAL colour TV 
systems. Three operating modes provide PAL colour bars, a five-step 
staircase with fixed-average picture level and the same staircase with 
variable a.p.l. 

The colour-bar output is a full field test signal appearing on every 
active line and consists of EBU 75"., amplitude, 100",, saturated colour 
bars in descending luminance order with white on the left and black 
on the right, PAL colour burst with four-field blanking sequence to 
CCIR specifications and composite sync and blanking. The staircase 
signal is keyed on during a selected line of the vertical blanking interval 
(lines 11-22 on field 1 or lines 324-335 on field 2). The last step— at 
white level — is double width so it can be viewed with and without 
subcarrier to detect clipping in the white direction. 

Normal PAL colour burst is provided on the staircase and colour- 
bar signals. The four-field burst blanking sequence during the vertical 
interval may be switched out if desired. A 1MHz reference signal 
frequency locked to the 4-4336 1875MHz PAL subcarrier oscillator is 
provided. The accuracy of the internal subcarrier oscillator may be 
conveniently verified by comparing the 1MHz reference with known 
frequencies e.g. Droitwich 200kHz transmissions. Outputs provided on 
the front and rear of the instrument are: composite PAL video, com- 
posite sync, subcarrier, horizontal drive, vertical drive, burst flag and 
reference signals of 12-5Hz, 25Hz and 1MHz. 



CCTV VIDEOTAPE RECORDER 

Recently announced by Ampex 
International, 72 Berkeley 
Avenue, Reading, Berks., is the 
VR-5103 closed-circuit videotape 
recorder. It is capable of record- 
ing and playback in the US 
standard of 525-lines at 60Hz as 
well as the European standard of 
625-lines at 50Hz. Working vol- 
tages are 80- MOV and 190-25GV. 
Fast forward and rewind time 
is 4 min. and remote control 
connections are provided for 
play, record and stop. The video 
frequency response is 3MHz and 
horizontal resolution is 300 lines. 



ANOTHER MULTIBEAM 

Following the introduction of 
their Multibeam aerials (Tele- 
topics March 1969) J-Beam 
Aerials Ltd. announce the addi- 
tion to the range of a smaller 
model, the MBM30. This consists 
of a Parabeam radiator and 
reflector with seven four-element 
multiple director units. The 
makers claim that the Parabeam 
radiator and reflector system with 
seven multiple director units has 
slightly superior performance to 
a Parabeam eighteen with little 
more than half the cross-boom 
length. The price is £3 15s. 



UK COLOUR TV LICENCES 

78,270 colour TV licences were 
taken out during 1968, the GPO 
announced recently. The monthly 
increase was about 8,000 in the 
final quarter of the year com- 
pared with 5,000 earlier in the 
year. 

COLOUR TV SET SALES TOP 
MONO IN US 

The Electronic Industries Associa- 
tion has produced preliminary 
figures for the 1968 sales of TV. 
radio, record and tape equipment 
by US manufacturers. All showed 
some increase over 1967 figures. 
Colour TV sales had a record 
year with sales up from 5-22 
million sets to 5-83 million. This 
for the first time was higher than 
monochrome sales. The total 
sales of monochrome sets 
advanced from 5-43 million to 
5-56 million. 

JAP COLOUR TV PRODUCTION 
For the nine months to Septem- 
ber 1968, Japanese statistics 
indicate that production of colour 
TV sets reached an all-time high 
of 1,779,131. This is a two-fold 
increase on the same period the 
previous year. 

Nearly 550,000 colour sets were 
exported to the United States by 
Japan in the year ended April 
1968. 

MULLARD 22m. COLOUR 
TV TUBE 

A 22in. ColourScreen television 
picture tube has been announced 
by Mullard Ltd. It is claimed to 
have a more rectangular and 
flatter faceplate than any other 
colour tube at present available. 
Coupled with the tube's push- 
through presentation, this makes 
for greater freedom in cabinet 
styling and viewing comfort. 



293 



LATEST ITA STATIONS 

The ITA announces that the new 
low-power TV transmitting 
station at Ffestiniog, Merioneth, 
North Wales was officially taken 
into service on February 28th. 
The station relays the Harlech 
TV programme for Wales from 
the ITA station at Arfon. 

The Ffestiniog station trans- 
mits vertically polarised signals 
on Channel 13, Band III. Effec- 
tive maximum radiated power is 
100W vision and 25W sound. 

Also announced is the trans- 
mitting station at Lethanhill, 
Ayrshire, Scotland, which came 
into service on January 31st. This 
station relays Scottish pro- 
grammes from the main ITA 
station at Black Hill The Lethan- 
hill station transmits vertically 
polarised signals on Channel 12, 
Band III. Effective radiated 
power (mean over the main arc) 
is 2kW vision. 

3-D COLOUR TV? 

The Japanese Toshiba Company 
has recently devised special lasers 
that can make colour images 
using argon and krypton gases. 
Their long-life makes the possi- 
bility of using these lasers for 
3-D colour TV a very real one in 
the future of TV. 



ECTT COLOUR COURSES 

With over 100,000 colour TV sets 
in use and over one million pre- 
dicted for two years' time the 
shortage of trained engineers is 
becoming quite acute and is likely 
to get worse. Courses run by 
technical colleges and the manu- 
facturers are heavily oversub- 
scribed and a new organisation 
has been formed to give intensive 
training to service engineers. The 
company is E.C.T.T. (Electronic 
and Colour Television Training 
Ltd.) of 45 Walton Road, East 
Molesey, Surrey. 

E.C.T.T. are running a number 
of courses for engineers of 
various proficiency and a pre- 
liminary course is even run on 
monochrome TV for those who 
need to brush up their knowledge 
before advancing to the very 
much more complicated subject 
of colour TV. For those unable 
to reach their training centre 
correspondence courses are being 
run and give the same training 
at a very reasonable cost. 



CONCORD SETBACK TV PREAMP BBC HANDBOOK 1 969 



The first back-of-set ultra broad- 
band preamplifier to be produced 
commercially has been intro- 
duced by Belling-Lee with the 
name Concord, Transistorised 
and mains-operated the new pre- 
amplifier operates on all tele- 
vision channels and f.m, radio 
in Band II. 

Housed in a grey moulded case 
approximately — 5 x 3| x 2ijn, 
Concord hooks on to the back of 
the domestic television receiver 
and is easily connected. 




Belling-Lee claim a signal 
increase of more than four 
times and report that perform- 
ance results are very good indeed, 

proving particularly useful in 
fringe or difficult reception areas. 
Recommended selling price is 
£7 7s. 



Now published at 7s. 6d. is the 
BBC Handbook for 1969. The 
Handbook records the activities 
of the BBC during 1968, includ- 
ing the commencement of the 
BBC-2 colour transmissions, and 
reviews the programme for 1969. 
Full details of the BBC organisa- 
tion are included, with Station 
lists, transmitter service area 
maps, etc. The Handbook is divi- 
ded into six main sections: Tele- 
vision; Radio; Programme Ser- 
vices and the Public: External 
Services; Engineering; Reference. 



BBC-1 & ITA IN COLOUR 

Entitled M What the Viewer needs 
to know" the ITA Engineering 
Information Service has issued a 
news sheet explaining the plans 
for programme duplication on 
u.h.f. The ITA co'our/625-line 
service is expected to open simul- 
taneously at Crystal Palace, 
Sutton Coldfield, Emley Moor 
and Winter Hill stations about 
mid-November, with Black Hill, 
Rowridge and Dover stations 
expected to come into service a 
few weeks later. 

This ties up with Lord Hill's 
statement in the BBC Annual 
Report published recently which 
suggests that colour/ 625-line pro- 
grammes on BBC-1 will start at 
the end of this year. 



LABGEAR UHFVHF SIGNAL STRENGTH METER 




Labgear Ltd., Cromwell Road, Cambridge, announces a transistorised, 
battery-operated portable u.h.f. /v.h.f. signal-strength meter covering all 
British TV channels in Bands I. Ill, IV and V. The chassis is anti- 
vibration mounted. An easy-to-read meter (25m V to ImV) is used and 
a plug-in attenuator is supplied as an optional extra. There is an auto- 
matic battery cut-out when the aerial feeder is withdrawn and the unit 
is fully stabilised against battery voltage variation. Size is 94 X 9\ X 
3|in. and weight 541b. 

The unit is provided with a carrying case and shoulder strap enabling 
the operator to make aerial adjustments while viewing the meter reading. 



294 



PART 7 
A1PRIESTLEY 



iNsmiiNG COLOUR 
serviginb RECEIVERS 

UNDERSTANDING COLOUR FAULTS 



WHEN you first start looking at colour TV 
you tend to be very impressed and 
uncritical. Then as you begin to gain 
experience you see pictures that do not look quite 
right but you are unable to say why. The difficulty 
lies in the fact that we have no absolute standard 
for comparison, and we have no means of knowing 
exactly what kind of picture is being transmitted. 
Test equipment is of no use to us where fairly 
minor faults are concerned because it will not 
measure the kind of colour differences which are 
small in themselves but important to the human 
eye. The only substitute is personal judgment. 
This takes time to acquire and is based on the 
stored impressions of countless pictures which 
looked convincingly right and of others which 
looked equally convincingly wrong. As time goes 
by the area between these two extremes gets 
smaller and smaller until the stage is reached 
where it is possible to view any receiver and pass 
an accurate judgment. You are then an expert, 
or at least partially so. You know that the colours 
are faulty, but you must also know what the 
fault is and whether it is in the transmission 
or inherent in the receiver, or can be cured. 

Here is a list of the basic faults in a colour 
receiver: 



(1) Unbalanced colours. \ 

(2) Incorrect ident. 

(3) PAL switch stopped. 

(4) Faulty Y (luminance) signal, J 

(5) Absence of R-Y, G-Y or B-Y] 

drives. 

(6) Absence of R, G, or B drives, i 

(7) No colour at all. 



Distorted 
colour 



Missing 
colour 



Tube Drive Techniques 

Before discussing how to set about diagnosing 
the cause let us first summarise the basic facts 
of colour life. Each gun of the c.r.t. is driven from 
two separate sources; the luminance and colour- 
difference channels. The luminance signal provides 
brightness information and the colour-difference 
signals provide the extra information which turns 
the monochrome picture into a full colour one. 
Thus a colour picture is in two parts as it were, 



and this is why it is impossible to get correct 
colour unless the monochrome picture is correct 
also. Figure 21 illustrates how the signals are 
applied to the c.r.t. „ 

Y- f=^ 



(a) 



Effective 
J q > drive 
J voltages 

I e J 



\}+* 



G-Y 



M 



B-Y 



IB] 

J I Effective 

■ e y drive 
j voitages 

,; bJ 
♦-♦-* 



M = Matrix (or Mixing) circuit 

(b) 



DC 



J. 

X 



Fig. 21 : Adding /urn/nance (Y) and chrominance (R-Y. 

G-Y and B-Y) information to obtain a colour picture, 

(a) Colour- difference drive, (b) Ft, G, B drive. 

The idea of adding extra information to a 
monochrome picture to turn it into a colour one 
is fairly straightforward, but there is an important 
point concerning the importance of negative 
colour-difference drive signals that deserves better 
understanding. Suppose wc have a monochrome 
picture and we want to make it slightly red. All 
we have to do is to turn on the red gun a bit 
more, so the extra information could consist of 
a positive contribution from the R-Y colour- 
difference channel. So far so good, but what is 
happening to the other two guns? 

Because the G-Y signal is obtained from mixing 
— (R-Y) and —(B-Y) signals in the appropriate 
proportions, pari of any signal we apply in the 
R-Y channel to get our red hue will appear in 
the G-Y channel also but not, of course, in the 
B-Y one. Our red signal is therefore going to 
be partially spoilt by the presence of some spurious 
green, giving an amber colour. 

In order to regain the pure red hue we originally 
expected it is necessary to provide a —(B-Y) signal 



in the B-Y channel. If this is of the correct 
amplitude it will appear in the G-Y channel as 
a signal equal and opposite to the unwanted R-Y 
one, and so will cancel it out. We therefore get 
no green output at the c.r.t. The —(B-Y) signal 
makes sure the blue gun is turned off by can- 
celling the luminance drive to the blue gun. Thus 
only the red gun is turned on. 

So a simple matter of providing a red colour 
on the screen of the c.r.t, has become quite com- 
plicated. Note particularly the importance of 
negative colour-difference signals : they are just 
as important as the positive-going ones. The 
example we have just described also illustrates 
the principle of transmitter encoding. 

An understanding of how luminance and colour- 
difference signals in combination drive a three-gun 
c.r.t. to produce a colour picture is one of the 
basic essentials of colour fault-finding. 

First Check on Black-and-white 

Before assessing a colour picture always check 
the monochrome picture first and make sure the 
grey scale is correct. Readjust it if necessary. 
This should be a compulsive routine procedure 
because small errors of grey scale will cause 
serious distortion to critical picture colours such 
as skin tones and will tend to invalidate any assess- 
ment of colour performance. This check also 
eliminates item (4) in our list of basic colour faults 
— a faulty Y signal. 

Unbaianced Colour 

Incorrect colour balance is probably the most 
common fault of all, but it may not come to your 
attention until the receiver develops a more obvious 
fault which causes the viewer to complain. Routine 
checking then shows that the colour performance 
is poor. Skies are too blue, or skin tones 
unconvincingly pink or green. 

There are two basic causes of unbalanced colour. 
The first one, which is less likely, is misalignment 
of the decoder causing incorrect R-Y or B-Y out- 
puts. It can be spotted immediately because arty 
error of this kind which is sufficiently bad to 
cause visible colour distortion will inevitably be 
accompanied by Venetian blinds. Blinds are sympto- 
matic of phase or amplitude errors in the delay 
line matrix circuits, or phase errors in the reference 
carrier to the R-Y or B-Y demodulators or other 
forms of crosstalk between the two channels. If 
blinds are barely perceptible then the decoder is 
operating correctly. 

The usual cause of poor colour balance in a 
picture is incorrect adjustment of the colour- 
difference drives to the c.r.t. The luminance drives 
to the cathodes of the three guns and the three 
first anode potentials have to be adjusted to cater 
for spreads in gun characteristics and different 
phosphor efficiencies in order to get a correct black- 



295 

and-white grey scale. For the same reasons it is 
essential to adjust the ratios of the R-Y, G-Y, and 
B-Y drives in order to get correct colour balance. 
Furthermore since G-Y is obtained by matrixing 
— (R-Y) and —(B-Y) signals the matrix adjustment 
(where present) must be checked in addition to 
the G-Y amplitude adjustment. The procedure for 
setting up the colour-difference drives has already 
been described in detail earlier in this series of 
articles (see Part 3). 

It is hard to over-emphasize the importance of 
correct colour drive. One hears so much about 
the need for good grey-scale tracking, and any 
errors are always so strikingly obvious, that one 
tends to concentrate on it to the exclusion of the 
equally important but rather more subtle defects 
of colour. Every time you see a picture which has 
poor colour performance but no component fault, 
first check the grey scale; then the colour-difference 
drives and G-Y matrix. Note the matrix. A small 
error will not produce an obvious and particular 
defect — just poor colour. This is especially true 
of skin tones. The G-Y matrix and amplitude 
settings are vital. 

If, having carried out the adjustments, the picture 
is still poor colourwise, the odds are at least 20 : I 
that the cause and the cure are the same as before. 
Do it again. And again if needs be. If you are 
still not satisfied recheck the grey-scale tracking 
and be very critical of the highlight colour tempera- 
ture. Is it illuminant C? You can only judge this 
in near total darkness because it will be distorted 
by the presence of artificial light or even daylight. 

In any ordinary, competent, design of colour 
receiver you must be able to get pretty good colour 
if these adjustments are properly carried out. 

incorrect I dent 

There are two main faults which can occur to 
a PAL switch mechanism. The switch will either 
be working in the wrong phase, or it will have 
stopped completely. If it is switching in the wrong 
phase it is obvious that the identification (or ident) 
process is not being carried out. This means that 
most colours will not merely be distorted but 
changed in hue in a particularly and clearly defined 
manner. There will not be any blinds on the picture. 
Once you know what to look for the diagnosis 
is easy. First the symptoms, then the explanation. 
If you look at the standard colour-bar test pattern 
you will find that an ident error produces the 
following effects: 

Correct Ident Wrong Idem 

White White 

Yellow Lime green 

Cyan Magenta (red /blue) 

Green Orange red 

Magenta Mid-blue 

Red Green 

Blue Mauve-blue 

Black Black 



296 



There is no halfway house with ident; either it 
is correct or it is not. 

The reasons for the hue changes can be seen 
from the vector diagrams of Fig. 22. Since the 

incoming After PAL C Corresponding 

signal switching 

Red! 



Correct 

ident. 



8-Y 



R-Y 
axis 



to the hue 
seen on CRT) 



Greenish 
Red 



R«n 



Both 
Line 1 
and Line 2 
give the 
correct 
hue of 
v Red' 



71 



(a) 



1\ 



Incorrect 
ident. 



Line 2 



7 7 

Greenish |r Greenish f 



Both 

Line 1 
and Line 2 
give the 
wrong 
hue Of 
"Green' 



(b) 

Fig. 22 : Vector diagrams showing why incorrect ident 
resu/ts in a hue which is the mirror image of the correct 
one. fa) Vectors under correct ident conditions, (b) 
Vectors under incorrect ident conditions. There are no 
blinds present on the picture when the fauit is incorrect 
ident. 

signal in the R-Y channel is being switched 180" 
(inverted) from line to line in sympathy with the 
transmission, the R-Y component of any particular 
hue being displayed will either be correct or inverted. 
The B-Y signal is not switched and so it stays the 
same regardless. Thus if the ident is incorrect a 
vector corresponding to a particular hue will be 
rotated about the B-Y axis to form the mirror image 
of the correct one. 

Wrong ident means one of two things: either the 
ident signal is at fault, or it is not operating properly 
on the bistable circuit. This is obvious, perhaps, 
but clear thinking is the basis for all efficient fault- 
finding. 

Tracing ident Faults 

To isolate the cause of the trouble connect a 
scope to the collector of the ident amplifier. This 
usually has a tuned circuit (at 7-8 kHz) and you 
will expect to see a continuous train of sinewaves 
of a peak-to-peak amplitude approaching twice the 
value of the effective h.t. rail. If the ident signal 
is absent or inadequate you have found the basic 



cause of the trouble. Connect the scope to the 
base of the ident transistor and see if an alternating 
train of trigger pulses is present. If so, the ident 
amplifier is faulty. If not, either there is a base- 
emitter short-circuit or the pulses are indeed absent, 
in which case you work backwards with the scope 
to find the fault. It cannot be far away because 
the a.p.c. loop is obviously in order (because colour 
is present on the screen of the c.r.t.) and this works 
off smoothed ident pulses derived from the burst 
demodulator. 

If ident is present at the collector of the amplifier 
then the fault lies in the coupling to the bistable. 
We know that the bistable is working, from the 
appearance of the picture. Again, there are only 
a few components to check, and the comparison 
diode in the feed to the bistable circuit is the first 
candidate. 

Once seen and understood ident errors are 
unmistakable. This is a case where a little experi- 
ence turns an apparently obscure fault into an 
easy one. 

PAL Switch Stopped 

It is important to be quite clear about the dif- 
ference between incorrect ident and a faulty PAL 
switch action. Ident trouble shows up as a major 
change of hue of all colours except those lying 
on, or close to, the + and —(B-Y) axis, i.e. blues 
and yellows. No extra blinds are caused. If on 
the other hand the PAL switch stops, a major 
change of hue will occur to these same colours 
(except blues and yellows) but the hue change will 
be different and serious Venetian blinds will be 
present. So the diagnosis is easy: hue change 
and no blinds — ident fault; hue change plus serious 
blinds — PAL switch fault. 

Hue changes caused by lack of PAL switching 
are as follows: 



Colour bars 


Hue Change 


White stays 


White 


Yellow becomes a striated 


Li me /Green 


Cyan becomes a striated 


Pale mauve 


Green becomes a striated 


Lime green 


Magenta becomes a striated 


Mauve 


Red becomes a striated 


Yellowish colour 


Blue stays 


Blue 


Black stays 


Black 



Each colour containing an R-Y component, which 
ought to be switched on alternate lines but is not, 
will consist of one line of the correct hue followed 
by one line of the mirror image hue as shown 
in the vector diagrams of Fig. 23. If you look 
closely you will be able to see the hue difference 
between consecutive lines of a field (or pairs of 
lines on the picture). A red hue will consist of 
two lines of red followed by two lines of green, 
and if you stand back a few feet the eye will integrate 
(add) these to give an overall impression of a 



297 



In com frig 
signal 



After the 
PAL switch 



- v0000000_/ 



Line 



B-Y 
axis 



Line 1 gives 
correct hue 
'Red' 



R-Y 
axis 



^h 



Line 2 gives 
wrong hue 
'Greenish' 



Alternate lines of a field are Red and Green in this example 
Fig. 23: Vector diagrams showing why a stopped PAL 
switch causes the overall hue displayed to be the sum of 
the correct one plus its mirror image, The individual hues 
can be seen at close range and cause severe blinds, 



greenish yellow. The same argument applies to all 
other colours in varying degrees, except +(B-Y) and 
— (B-Y), which contain no switched component and 
so remain unaffected. 

If you want the simplest possible diagnostic test, 
here it is: red goes to green — ident fault; red goes 
to dirty-yeilow plus blinds — PAL switch fault. 

Tracing Faults in PAL Switch Circuits 

Once again there are not many circuits involved 
in the PAL switch system of a normal design of 
decoder. A line pulse is fed through a pair of 
gating diodes to two transistors forming a bistable 
circuit and the square wave outputs from the two 
collectors are fed via two switching diodes to the 
primary of a coupling transformer together with 
the reference carrier. The switched carrier output, 
inverted from line to line, appears across the 
secondary. An oscilloscope is essential for rapid 
fault-finding. Check the following: (1) Are line 
trigger pulses present and reaching the transistors? 

(2) Is a square wave output present at each collector? 

(3) Is the square wave getting through the switching 
diodes? (4) Is a switched subcarrier output present 
at the transformer secondary? (5) Is there a 
reference carrier input to the switching transformer? 

Somewhere along the line there will be an 
absence of line pulse, square wave, or reference 
carrier and this will isolate the cause of the trouble 
to a very small area of circuitry. See Fig. 24. Some 
notes later on in this series about tracing faults in 
individual circuits may come in useful when fault- 
finding in a bistable circuit. This may be new 
to many engineers, but being a go/no-go device it 
should not present much difficulty. 

In some decoders the PAL switching is controlled 
directly by the ident amplifier without a bistable 
circuit being used; in others a ring modulator 
instead of a pair of switching diodes is used in the 
input circuit to the coupling transformer. 




Line pulses 



Fig. 24: A typical bistable PAL switch circuit. Five quick 

checks with an oscilloscope at the points shown will 

isolate the fault to a particular part of the circuit. 

Next month we shall complete this outline of 
colour faults by dealing with the effects of faulty 
Y and colour-difference drive signals and then turn 
to the symptom of no colour and how best to 
track down quickly the cause of this trouble. 

TO BE CONTINUED 



Readers are invited to attend the Practical 
Wireless and Television Filmshow and 
Lecture at the Caxton Hall, Caxton Street, 
Westminster, London, S.WJ, on Friday, 
March 28th 1969 at 7.15 p.m. 

The Lecture is about Colour Television 
and covers the setting-up procedure, dealing 
in detail with degaussing, purity, convergence 
and grey-scale tracking. The film is entitled 
"It's the Tube that makes the Colour" and 
describes the manufacture of Milliard 
" ColourScreen" TV picture tubes. 

Free refreshments will be served during the 
interval and free tickets may be obtained by 
sending a stamped, addressed envelope to: 
FILM SHOW, Practical Television, IPC 
Magazines Limited, Tower House, 
Southampton Street, London W.C.2. 



298 




THROUGH the eye of an RCA 4-51b. TV camera 
millions of viewers around the world 
journeyed with the three astronauts on their 
Apollo 8 flight. The miniature TV camera, the 
result of two years' intensive work and experimenta- 
tion by RCA, is an exact duplicate of the RCA 
camera which sent back the live TV pictures during 
the Apollo 7 earth orbit mission last October. 

According to the Programme Camera Manager of 
RCA, Richard P. Dunphy, the Apollo 8 camera is 
a forerunner of even smaller TV cameras which ar^ 
at present being developed for use when man lands 
on the moon, possibly later this year. 

Transmission 

The output from the Apollo camera was fed into 
a premodulation processor where it was frequency 
multiplexed with telemetry and voice data. The 
video was then fed into an S-band omni-aerial for 
near-the-earth transmission or to a high-gain S-band 
aerial for transmission from outer space. Electronic 
signal processing systems were situated at Merritt 
island, Florida; Corpus Christi, Texas; Goldstone, 
California; and Madrid, Spain. Goldstone and 
Madrid were the stations receiving TV from the 
spacecraft. Here the signals were processed and 
relayed to the National Aeronautics and Space 
Administration Manned Spacecraft Centre for release 
to the major TV networks of the world. 

Camera 

The tiny TV camera developed by RCA for 
N.A.S.A. uses a 160° wide-angle lens for on-board 
monitoring the astronauts and a 100mm. lens for 
viewing scenes outside the spacecraft. The use of 
integrated circuits enabled engineers at the RCA 
Space Centre in Princeton, New Jersey to make the 
camera some thirty times lighter and eighty-five 
times smaller than a standard black-and-white TV 
broadcast camera. And the Apollo 8 camera needs 
only 6W of power to operate compared with 500W 
needed for a studio camera. 

As television viewers could see some difficulty was 
experienced with high light levels and stability of 
picture and the telephoto lens was not as simple to 
use as it should have been. However, considering 
the extremely difficult conditions under which the 
pictures were taken they were of very good quality. 



ML Jfel 






Bandwidth 

Because of the necessity to conserve weight, size 
and power together with the enormous distances 
the TV system used scanning standards different from 
those of normal broadcast TV. RCA developed 
the necessary ground station scan converters for the 
earth receiving stations. US commercial broadcast 
TV transmissions have a signal bandwidth of 
4-5MHz (525-line system) but because of the space- 
craft limitations Apollo's TV system was designed 
to operate with a 500kHz bandwith. This nine-to- 



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299 



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one reduction resulted in substantial saving in tele- 
casting power but necessitated a field rate of 20 per 
second with 320 lines. 

Standards Conversion 

The signals received from Apollo 8 were applied 
to a TV display focused on to a broadcast vidicon 
camera and stored on the tube's photoconductive 
target. During each sixth broadcast field (US 60Hz 
field rate) the camera read out one field of video 
signal at the broadcast rate, the scanning beam 
of the camera being " gated off" during the next 
five broadcast scanning fields. The video signal field 
read out by the camera was fed to a magnetic disc 



recorder (a similar unit to those employed for 
" action replay" shots in TV sports broadcasts). 
The recorded broadcast-rate field then passed a read- 
out head and was read out five times before a new 
one was received from the vidicon camera and 
recorded. In this way conversion to the broadcast 
field rate for normal transmission was achieved. 

Transmission Programme 

In all six TV transmissions were beamed to the 
earth from Apollo 8. Two were transmitted en route 
to the moon, two from lunar orbit and the other two 
on the return journey to earth. 

The third and the fifth television transmissions were 




Were can be seen one of the 
technicians testing the tiny TV 
camera prior to the Apollo 
mission. 



300 




William Anders shows TV viewers his toothbrush during 

the first live transmission from the spacecraft on 

December 22 from a distance of 1 39,000 miles from the 

surface of the Earth. 

processed by the Spanish receiving station the other 
four being dealt with at Goldstone in California. 
The signals received in Spain were relayed to the 
Spanish earth station at Buitrago which then sent 
them across the Atlantic via Intelstat II F3 (Canary 
Bird) to Andover, Main and on to the Houston 
Space Centre via New York. It was the Spanish 
station which transmitted the pictures to Brussels 
for transmission over the Eurovision network. 

The television camera used in Apollo 8 and the 
ground equipment at all locations except Corpus 




This is one of the photographs that the asL-onauts took as 

they orbited the moon. The view is to the north west and 

includes the Gauchy Scarp in the foreground and rills in 

the background with the Gauchy Crater between tftem, 

Christi were produced by RCA's Astro-Electronics 
Division. The scan converters were built under 
contract to N.A.S.A., the converters at Goldstone, 
Madrid and Merritt Island being newly delivered 
systems enabling N.A.S.A. to provide live TV from 
spacecraft for broadcast by the TV networks. 

The RCA Space Centre also developed the camera 
systems used aboard the Ranger satellites which took 
the first close-up photographs of the moon's surface 
and the cameras on the Tiros, Essa and Nimbus 
weather satellites. ■ 



LATEST BBC-2 STATIONS 





Hannington: Channel 45, horizontal polarisation. 



, 



Mendip: Channel 64, horizontal polarisation. 



301 




SERVICING 

tteleviSion 
receivers 

L LAWRY-JOHNS 
THORN 950 AND 960 CHASSIS 



THE 950 chassis employs a very similar circuit 
to the 900 chassis which was the subject of a 
previous article in this series (see August and 
September 1968). However, variations to the basic 
chassis and differences brought about by the intro- 
duction of the semiportable models warrant further 
discussion. 

The main electrolytic capacitor unit seems to be 
failing more regularly now, giving rise to various 
symptoms from poor sync, curved verticals, dto- 
nounced hum etc. to more obsure troubles such as 
weak field lock on 625 only (check the video stage 
carefully before changing the block however). 

The block itself is on the right-hand side and 
has five wrap-round tags. When fitting a new unit 
the leads should be soldered otherwise they will 
almost certainly fracture if an attempt is made to 
rewrap them. The correct replacement capacitor 
will have the colours clearly marked to coincide 
with the leads except the chassis tag which is plain. 
The screening division member which is across the 
chassis is secured by a screw on either side and 
removal of this and the PY800 makes access to the 
smoothing block easier. 

Line output stage 

C98, C99 and CI 06 have proved troublesome, the 
first two causing no line scan or excessive width 
depending upon which fails and on what standard, 



whilst CI 06 shorts when the receiver is switched to 
625 causing the timebase to cease functioning with 
probable damage to the v.d.r. (Z3). 

An annoying effect is sometimes encountered and 
takes the form of a ripple on the picture according 
to the setting of the brilliance control. This is 
usually due to a fault in one of the e.h.t. rectifiers. 
The complete tray should be replaced. This is of 
course the tray which carries the three X80/150 
pencil-type rectifiers. 

Field timebase 

Uncontrollable field roll can usually be traced to 
C79 (0003 /<F). The working voltage of this 
capacitor is very important and nothing under 1,000V 
should be fitted. 

Striations 

These are vertical rulings, mainly obvious on the 
left side. Check W9 (OA81), the lead to tag 51 and 
the winding H-J on the line output transformer. 

Lack of contrast 

This can be due to a large number of factors but 
in making checks do not omit to try a replacement 
30FL14 (PCF808) in the V4 position. Quite often 
attention is concentrated on the tuner unit and video 



PRINTED 
BOARD 
SERVICING AIDS 

Printed wiring between 
components is shown by 
colour-coded lines printed 
on the component side of 
the board. 

White— Heaters 8, AC 

Blue — Earth 

Blue & White — Cathodes 

Green — Gridi & AGC 

Red A Green — Screen Grids 

Red & White — Anodes 

Red— HT 

Broken Red-Decouple J HT 

Red & Blue — Boost HT 

External connections to 
wire-wrap lags numbered 
to correspond with circuit 
diagram are also shown. 



LINE LINEARITY 
CORRECTION SLEEVE 



MAINS ADJUSTMENT 



FUSE J-SA 

625 LINE HOLD- 
UHF CONTRAST- 
FRAME HOLD- 
405 LINE HOLD - 
VHF CONTRAST - 

nrrrn 




PICTURE SHIF 



PIN CUSHION 
MAGNET 



FUSIBLE 

RESISTOR 

(HT) 



UHF AERIAL 
VHF AERIAL 

Ratio Detector 
1 1 >^6<ilanct (625) 



oi Main * ' \ 



Toi Main 
Frami Linearity 




Local/Distant width Focm 

Fig. 1: Hear chassis view, showing preset adjustments. 



302 






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303 



HT+ 



On/pff 
switch 




S1 solenoid S2 solenoid ^^% 

Fig. 3: Heater and h.t. circuits. Thorn 950 chassis. Note that different heater circuitry is used on the semi portable mode/s 
This wiii be shown next month. St, L43 and L44 are on "plus radio" versions. 



stage, the vision i,f. being neglected. So check V4 
and also check R28 (5kQ) which changes value quite 
regularly. 

Tube faults 

The majority of other common faults were out- 
lined in the previous article including mention of 
low emission. We would however point out that 
many tubes have been condemned when in fact a 
check at pin 3 of the tube base would have revealed 
a low voltage. The supply resistor is R121 (3-9MH) 
and this is decoupled by C93 (0-ImF), C93 can 
become leaky or short completely, virtually shorting 
the tube first anode to the h.t. line. 

It is far from unknown for the tubes to develop 
two other defects which would normally cause thern 
to be discarded. The fact that a tube has an open- 
circuited heater is usually regarded with head 
shaking as " well, that's it." This is not necessarily 
so. Quite often the internal break in the heater can 
be welded by the application of a brief pulse from 
the top cap of the PL500. 

We hasten to add that this operation must be 
very carefully carried out for several reasons. The 
first is the possibility of damage to the person doing 
the job, the second the possibility of damage to the 
line output transformer and the third the probability 
of destroying the tube heater completely. 

The operation should be carried out as follows. 
Remove the tube base socket. Short pins 1 and S 
of the socket to preserve heater continuity. Connect 
a lead from pin 1 of the tube base to chassis. 
Allow the set to warm up. Using a very well insu- 
lated lead, touch one end to the PL500 top cap 
and the other to pin 8. An arc will be seen inside 
the tube neck. Do not repeat unless it can be 
proved that the heater is still open-circuit. Only 
the briefest of brief touches is required. By this 
means tube replacement may in some cases be post- 
poned for a considerable period. In others the 
operation may be quite unsuccessful. This pulse 
application is often recommended for clearing shorts 



but not so often for internal welding of open-circuit 
electrodes. 

The other common defect causes a very very dim 
raster to be displayed which is completely unaffected 
by operation of the brilliance control. This indicates 
an open-circuit grid. Proceed as before but join 
pin 7 (cathode) to chassis instead of pin 1. The 
pulse should now be applied to pin 2 or 6 (both 
grid). If successful this may not only restore full 
control of brilliance but also a marked increase of 
emission due to the disturbance of the cathode 
coating. Considering the alternative of discarding 
the tube completely, this is indeed a bonus! 

Solenoid switching 

The foregoing notes apply equally to the 900 and 
the 950 chassis. The main differences concern the 
system switching and in the case of the 960 semi- 
portables the heater supply. The mechanical opera- 
tion of the system switching in the 900 chassis was 
replaced by solenoids. In the 950 models these 
are mounted on the right side so that they push or 
pull the bar along. They are energised by the supply 
switch S4 on the rear of the v.h.f. tuner and 
de-energised by S2N on the system switch. 

$4 is fed from the on/off switch via R147 (100f>) 
which is there not only to limit the current through 
the solenoids but also to operate the cut-out in the 
event of a short or failure of switching in the 
solenoids. The cut-out is reset by joining the two 
wires and applying a soldering iron. Do not wrap 
a wire round the join as this could cause quit; 
serious damage. 

The writer has on more than one occasion found 
that the receiver functions perfectly well on 405 but 
that R147 becomes overheated and opens the cut-out 
when switched to 625. This has been found to be 
due to the orange lead to the actual solenoid being 
pinched under the chassis with the insulation 



— continued on page 311 



304 







■^B" 












j 
J 




Wake up trade ! 

Congratulations on your hard-hitting editorial 
(Practical Television — February issue). 

I endorse your comments and can only hope that 
the trade will ** wake up " in time to cash in on 
Colour. — R, i, le H. Powditch (Electronic & Colour 
Television Training Limited, Surrey). 

Converting 405 sets to 625 

I have read with interest the articles by K. 
Cummins in the January and February issues on 
converting 405-line sets for 625-line reception and 
if the steps described are taken I am sure that the 
end results will be first class. But I would like 
to mention that with the right type of receiver con- 
siderably less need be involved to achieve good 
BBC-2 operation, using only a u.h.f. tuner and 
eliminating the conversion kit. To illustrate my 
point I quote my own experiences. 

I was particularly lucky in obtaining a second- 
hand Ferranti T1001 14 in. receiver for £2 10s. Od. 
some time ago. After replacing the U25 e.h.t. rec- 
tifier this was in excellent working order and I found 
it to be extremely adaptable and versatile. It will 
receive BBC-2 as well as the ITV and BBC-1 pro- 
grammes with little more than the addition of a 
u.h.f. tuner. 

The circuit of the receiver is basically unchanged 
from when it was new some 12 years ago. The 
range of the line hold control had to be increased 
of course and this was easily done by shorting across 
the 270 kil resistor in series with it. The result is 
that the range now covers from 405 to 819 lines + ! 
On one occasion I did manage to resolve a com- 
plete 819-line French picture on Channel 8 during 
an evening of freak reception, albeit somewhat lack- 
ing in brightness and width. However for 625-line 
operation it is excellent with plenty of brightness 
in hand, adequate width and good stability. 

As regards the introduction of the u.h.f. signal 
to the receiver stages, the u.h.f. valve tuner needed 
slight modification of the oscillator section and the 
i.f. coil in order that the output frequency matched 
the lowest frequency in the v.h.f. tuner, i.e., 
Channel 1. When switched to this channel the out- 
put cable from the u.h.f. tuner is plugged into the 
aerial socket of the set and the v.h.f. tuner in effect 
acts as extra i.f. stages, the fine tuner being adjusted 
to get the best sound consistent with vision. This 
is done of course after the u.h.f. tuner control is 
adjusted to the correct channel. 

Due to the fact that the sound and vision 
characteristics of the new standard differ from the 
old one it may seem surprising that anything is 



received at all by this means. However by a little 
fiddling around it is amazing what can be achieved. 
To resolve the sound at good strength I found that 
substituting the 30F5 first sound i.f. valve with an 
EF184 and slightly adjusting the sound i.f. coil slugs 
did the trick, and the fact that on u.h.f. the sound is 
♦frequency modulated does not affect the quality. 

The vision section was no more difficult to adapt. 
The negative picture problem was very easily solved 
without alteration to the circuit. This set is of the 
type whereby the picture will turn negative by over- 
loading if the contrast control is turned up beyond 
a certain point, therefore I reasoned that if a posi- 
tive picture can turn negative by this means, why not 
vice versa? {This is of course assuming that the 
signal strength is sufficient to cause the set to over- 
load, as is the case in my locality.) This in fact 
does happen and in practice the control has to be 
turned down some way from maximum, as does the 
volume control, otherwise the picture becomes un- 
stable and the speaker resonates with a loud whistle. 
The vision i.f. coils were also slightly retuned as a 
final step to ensure that good sound and vision are 



To VHF aerial 



To BBC 2 
i set -top 
aerial 



Earth to Receiver chassii. 



L UHF 

tuner 



° 5<> V, 



4 

625. 



HT+ 



405, 
625. 



Resistor to 

/ maintain 

neater 

balance 



Tuner 
* series 
heaters 



405, 



M2o 



*<, 



UHF valve heaters 
wired in series 
with Receiver 
heater cha-n 



IF output to Receiver aerlai socket 
(mean frequency approx. 40 MHz) 

■»- VHF aerial to Receiver aerial socket 



Fig. 1: Simple 405-625 power switching arrangement. 

405 c 



HT+ to UHF tuner 



°>£ 



S1a to Receiver HT line 




To IF coil on UHF tuner 

Fig. 2: Suggested system using multisection switch. 



305 



consistent with each other. Any further adjustment 
can be made by the v.h.f. fine-tuning knob on the 
receiver. 

After the steps I have described were carried out 
I fully expected the BBC-1 and ITV reception to 
have suffered but apart from the tuning being more 
critical the quality is more or less the same as 
before. Of course what must help considerably is 
the fact that I live in a favourable locality where 
the signal strength of all three stations is high, being 
situated only about 5 miles from the Tacolneston 
transmitter (Channels 3 and 55) and 20 miles from 
Mendlesham {Channel 11). 

When changing from one system to another I 
use a simple power switching arrangement which 
I have illustrated (Fig. 1), plug in either the v.h.f. 
aerial or the u.h.f. tuner i.f. output, whichever is 
needed, reset the contrast and line hold controls and 
for some strange reason increase the height for 405- 
lines and reduce it for 625-lines. I see no reason 
why these operations cannot be carried out simul- 
taneously by the use of one multisection switch 
(Fig. 2) and a few preset resistors, but so far 1 have 
not tried this. 

This set performs very well using a home-made 
set-top BBC-2 aerial and apart from an initial warm- 
up drift, which can be corrected by the v.h.f. fine 
tuner on the set, will give good steady results for any 
length of time. 1 have used this set successfully in 
this manner for nearly two years now with no trouble 
save for one fuse blowing and the need to replace a 
faulty valve in the v.h.f. tuner. When you consider 
the age of the set and the extra demands made upon 
it I feel it does credit to the "old timers" and it 
shows what can be done with the minimum amount 
of alteration and cost with the right sort of set. The 
cost of the set and the conversion materials amounted 
to less than £5. — M. G. Jackson (Norfolk). 

(We feel you have struck lucky with this chassis! For 
others wishing to try this conversion the F err ant i 
Model T1002 is the J7in. equivalent while Ekco 
models fitted with a similar chassis include the T326, 
T327, T330 and T344. Many other later Ferranti and 
Ekco models were fitted with simitar chassis. — Tech- 
nical Editor.) 

I am writing concerning your articles on 405 to 
625 television conversion. I carried out this type 
of conversion on three receivers when BBC-2 started 
in 1964 and they are still giving good service. I feel 
that Mr. Cummins has made the conversion sound a 
bit complicated with line blanking and brightness 
equalisation which I have not found necessary. Also 
when feeding the a.f. from the 625 i.f. board to the 
volume control — why not leave the volume control 
where it is if it is already in the triode grid circuit 
because all you have to do on 625 is to turn the 
volume control down? 

Regarding increase of h.t, for the line timebase 
again I have found this unnecessary. From my 
experience the heater of the e.h.t. rectifier is under- 
run on 625 rather than over-run causing lower e.h.t. 
which alters the focusing and increases the height. 

My own set, a Decca DM17, has been working 
under these conditions for four years. 

I would be willing to help anyone who wants to 
perform this conversion and comes up against prob- 
lems. — A. H. Rusbton (London). 



These bands are ours ! 

From a report appearing in The Engineer for 
11th October 1968 it is understood that Mr. J. R. 
Brinkley of STC is urging that the lower limit of 
the u.h.f. band allocated to business radio should 
be extended downward from 450 to 420MHz. 

The bands from 425-429MHz and 432-450MHz 
are and have for many years been allocated on a 
shared basis to the Amateur Service and other users. 

This portion of the spectrum which Mr. Brinkley 
wishes to annexe is extensively occupied both by 
communications stations and some 70 privately 
owned television transmitters in all parts of the 
United Kingdom.— D. S. Reid (P.R.O. British 
Amateur Television Club). 

What's wrong with the trade ? 

I have read your editorial (February) with interest 
and would like to point out the following facts: 
(I) There has over the past 12 months been a drastic 
shortage of new sets to small retailers. (2) Faulty 
new sets from the manufacturers have been the rule 
rather than the exception— at least this is my 
experience — and if this is so with monochrome sets 
I shudder to think of the colour sets. 

During a recent conversation with a manufacturer's 
service department I was advised to leave colour alone 
for at least another year for the following reasons: 
(1) None of the manufacturers have produced a 
reliable set. (2) At the end of this year all will go 
ahead and produce single-standard models, (3) The 
initial cost of equipping a service department is 
between £600 and £1,000 and will take too long 
to recoup. (4) When TV engineers are paid a reason- 
able rate for their knowledge and work you will get 
good engineers to stay in the trade and not lose them 
to industry or other jobs. 

It is time the idea that a service department is 
lucky to break even was disposed of and the engineer 
paid what his skill and experience deserve, and that 
a service department was admitted to be a paying 
proposition. 

There is at present no foreseeable bonanza and the 
unreliability of new sets, not only colour but mono- 
chrome, make it a very hazardous business for the 
small man, with S.E.T., C licence, road tax, wages 
and all the rest. The TV business is no good to any- 
one other than the rental organisations who I think 
indulge in colour mainly for prestige. 

In closing I would suggest that it is time that TV 
engineers had their own trade union separate from 
any other. — S. G. Woodbridge (Middlesborough). 



PRACTICAL WIRELESS 

In the MAY issue 

COMPREHENSIVE TRANSISTOR 
TESTER 

Constructional feature: tests gain and leakage of small-signal 
and power types, both npn and pnp. 

PULSE CIRCUITS 

Stan of new series explaining the principles of transistor puise 
circuitry. Part 1 deais with the use of transistors as switches. 

On sale April 8th 



306 



VALVE & COMPONENT 

OVERHEATING 



PART 2 



PROBABLY the most common case of valve 
overheating outside the line circuit is that 
of the field output pentode, a PL82, PL84, 
PCL82 or PCL83 in older receivers and a PCL85 
in current models. Coincident symptoms are 
insufficient height with a cramped base to the raster 
that progressively gets worse as valve temperature 
becomes excessive. In most instances valve replace- 
ment will be found to work at normal temperature 
and cure all symptoms, but in many cases it will be 
found that valve failure was precipitated by a reduc- 
tion in the value of the bias resistor thereby causing 
excessive anode current which in turn further 
reduced the value of the cathode resistor. Obviously 
unless the cathode resistor is replaced by one of 
correct value the new valve will be short lived and 
also produce the symptoms in a milder form, the 
extent depending on the resistor's value change. 

When making voltage tests it is easy to assume 
that the grid coupling capacitor from the anode 
of the triode generator is leaky since usually a 
distinct positive voltage will be found on the pentode 
grid. However, even a new pentode running for 
some time grossly underbiased can develop a posi- 
tive grid potential due to the liberation of gas 
molecules from the electrode structure making the 
valve slightly soft. To show that such a positive 
voltage has not leaked through the grid coupling 
capacitor, remove the valve, short the valveholder 
heater pins with a 5012 resistor or wire link, then 
check the grid socket for positive voltage on sub- 
sequently switching on. Only extremely rarely will 
there be a d.c. potential present to prove the capa- 
citor faulty. 

Automatically, therefore, when the field pentode 
runs excessively hot check the cathode resistor for 
being mainly of carbon composition they reduce 
in value after years of service or when subject to 
abnormal current- 
Audio & video output valves 

The same reasoning applies to sound output 
pentodes, and to the PCL83 in particular. When- 
ever sound distortion occurs and this valve is run- 
ning excessively hot, measure the value of the 
cathode resistor. 

As with line output pentodes, failure of anode 



G.R. WILDING 



voltage will result in a screen current sufficiently 
high to make the screen grid winding glow, but as 
this would usually be the result of an open-circuit 
transformer primary winding— a very rare occur- 
rence — it is seldom evident. 

In older receivers employing an EF80 video 
amplifier internal short-circuits, especially from grid 
to screen, were quite common and generally resulted 
in the screen feed resistor, vision diode and video 
cathode resistors all being burned up. However, 
the PCL84 valve that generally superseded the EF80 
in this stage and the PFL200 now commonly found 
in current dual-standard models are free from such 
interelectrode shorts. 

Heater-cathode shorts 

Cathode-heater short-circuits, particularly in valves 
or rectifiers with large heater voltages and placed 
high in the heater chain, are a common cause of 
the mains dropper resistor drastically overheating 
and of course also over-running the heaters of all 
the valves between the a.c. feed from this resistor 
and the defective valve. Furthermore, if the faulty 
valve has a cathode resistor, this will also be burned 
up. 

Quite often if incorrect receiver fuses are fitted 
the severity of a heater circuit short-circuit will 
burn out a section of the dropper resistor or cause 
the thermistor to crack and thus disconnect the feed. 
Even if not burned out, a prolonged and heavy short- 
circuit current will invariably damage the component 
so that the lead-out wires make only imperfect or 
intermittent contact while the body of the com- 
ponent will crumble at the least pressure. 

Heater circuit silicon rectifiers 

In those receivers employing a silicon rectifier in 
series with the heater circuit a short-circuit in this 
component will cause all the valves to be grossly 
over-run and may continue to do so without the 
set user being really aware that a fault condition 
exists. Picture brilliance, contrast levels and volume 
will all be above normal but without any real defect 
being apparent, although in some models the exces- 
sive temperature of the sound output valve may pro- 
duce sufficient distortion for the owner to complain 
about it. 



307 



In those Bush-Murphy models 
using a BY101 in this arrange- 
ment, however, it becomes im- 
possible to use the receiver 
should this rectifier develop a 
short - circuit as uncontrolled 
field slip will develop. This fault 



indication is accomplished ty Fig. Z: Heater circuit with rectifier used in the Thorn 9W chassis. Bias for the 

feeding the screen of the sync field output pentode (30M.14) is tapped from the unidirectional (pulsed-d.c.) 

separator from a point on the heater current and smoothed by 83 and C2. 
rectified heater chain (after the 




necessary smoothing by a CR combination) instead 
of via a dropping resistor from the h.t. rail. Should 
the BY 101 develop a short-circuit the heater current 
will be pure a.c. and the voltage at the sync separator 
screen will then also be a.c. instead of d.c. thus con- 
stantly tripping the field timebase. When the BY101 
is replaced, therefore, correct polarity must be 
observed, that is with anode to the a.c. feed from the 
dropper resistor to provide the necessary positive 
output from its cathode. 

Field output stage bias 

In the Thorn 980 series of portable models a 
BY 101 is placed in the heater chain (see Fig. 3) 
to reduce heat dissipation inside the cabinet, but 
this time with connections reversed to give a nega- 
tive rectified output. Polarity is reversed to provide 
a negative bias for the pentode section of the 
30PL14 field output valve without the need to 
include a resistor in the valve's cathode lead. This 
has two advantages. First there is a worthwhile 
gain in effective anode h.t. since any bias developed 
across a cathode resistor must be deducted from 
the available h.t,, while secondly the absence of a 
cathode resistor and decoupling capacitor ensures 
that there can be no negative feedback loss from 
this point. Should the BY10I go short-circuit in 
these models absence of bias plus the simultaneous 
injection of a small a.c. voltage to the pentode grid 
would immediately result in reduced height and bad 
linearity to instigate a service call. 

It must not be assumed that BYlOOs or BYlOls 
often break down in this heater circuit usage, but 
the possibility must always be considered. 

Mains dropper safety precautions 

A point worth noting in these Thorn portable 
receivers is that the mains dropper resistor is split 
into two sections, one of 52D in the conventional 
position and the other of 11012 placed immediately 
after the first two valve heaters (the usual boost 
rectifier and the line output pentode). Of all valves 
these two are most likely to develop a heater-cathode 
short-circuit and by placing them after the heater 
circuit BY 1 01 any short-circuit current would be 
limited only by the rectifier's forward resistance plus 
the 52H resistor in its cathode lead. Such a heavy 
current would blow the fuse with more certainty 
than if the HQQ section was also included in the 



feed to these two heaters and at the same time this 
latter resistor is completely protected from possible 
damage unless other valves lower in the heater chain 
break down. 

Hybrid receivers 

In hybrid receivers where Lhe transistor power 
supply is developed across a resistor or resistive 
network at the earthy end of the heater circuit a 
short in the BY 101 would raise this transistor l.t. 
supply although since the resistance of the valve 
heaters would be raised by the excessive current 
they would absorb the greater proportion of the 
excess voltage. The effect would be much more 
serious if the resistor across which the transistor l.t. 
supply developed went open-circuit, for then almost 
the full mains voltage would be developed across 
the resistor and thus also across the transistors. 
Fortunately the electrolytics shunted across the 
transistor l.t. rail and chassis are of low working 
voltage and would certainly break down under the 
greatly increased voltage thus virtually short- 
circuiting the l.t. rail. 

HT shorts 

When surge lirniters moderately overheat with 
only a small reduction in rectified h.t. voltage the 
almost certain cause is a partial short-circuit across 
the h.t. rail. This could be due to a variety of 
causes It could be an internal short-circuit in a 
valve, with the shorting electrode fed via a medium- 
value resistor from the h.t. rail, a short-circuit 
decoupler similarly resistive fed from h.t., or a 
shorting solder blob in a printed circuit receiver. 
The first move is to look for charred or discoloured 
resistors: this will generally reveal the defect quicker 
than meter tests. 

When the surge limiter gets red hot, implying that 
the short-circuit is directly across the h.t. rail before 
or just after the series smoothing choke, it is essen- 
tial to locate the cause with the set switched off 
to avoid permanent damage to the rectifier. The 
surge limiter will need replacement anyway other- 
wise it is sure to go open-circuit within a short time. 
The first move is to determine whether the short- 
circuit is greatest on the rectifier or set side of the 
smoothing choke. If greatest at the rectifier end 
the only possibility is that the reservoir capacitor is 
defective, but if as usually occurs the short-circuit 



308 







Fig. 4; Typical heater and h.t. power supply circuits. When testing for leakage 

across the h.t. rail and chassis remember that if the ohmmeter applies a negative 
potential to the SV100 cathode this will be forward biased and conductivity will 
be measured through the BY1 00 and heater chain as we/las through any leakage. 



is on the smoothed end there are many possibilities. 
One of the main smoothing capacitors may be 
short-circuit but as electrolytic failures are rare 
look for charred resistors, but this time of low value 
and feeding h.t. circuits. It is possible for the wind- 
ing of the smoothing choke or the primaries of the 
sound or field output transformers to short-circuit 
to core, but these possibilities are also rare. Instances 
do, however, occur, usually shown up by melting 
wax caused by the overheated winding. 

Some internal valve short-circuits can put almost 
a "full" short-circuit across the h.t. rail, but to do 
so the electrodes concerned must be connected via 
low-value feeds to h.t. and chassis respectively. This 
usually implies an if. pentode or field or sound out- 
put valve, for in all these instances the anodes are 
connected via the low d.c. resistance of a transfor- 
mer's primary winding to the h.t. rail — plus a low- 
value decoupling resistor in the case of an i.f. pentode 
— screen-feed resistors are all low while the cathodes 
terminate at chassis via the usual low-value bias resis- 
tor. The best method of locating a defective valve is 
simply to connect an ohmmeter across the h.t. rail 
and chassis and note if removing any valve "pos- 
sibles" removes the short-circuit. 

When tracing short-circuits in receivers with BY100 
type rectifiers, however, it becomes easy to make 
incorrect assumptions. For instance if the polarity 
of the ohmmeter battery is such that on applying the 
test-prods across the h.t. rail and chassis the rectifier 
is forward biased current will pass through the rec- 
tifier and will also flow through the valve heater 
chain (see Fig. 4). This means that with the ohm- 
meter applied one way round it could indicate a value 
of well under IkO across the h.t. rail and chassis 
when really it is measuring the resistance of the 
heater circuit plus the forward resistance of the 
BY 100. To further complicate matters and cause 
confusion on removal of any valve this reading will 
revert to the true leakage across the h.t. rail since the 
heater chain will then be broken. One could easily 
form the impression therefore that there was an 
internal short-circuit in the valve removed. This 
could not of course happen with a valve h.t. rectifier, 
but to eliminate this very real possibility always 
reverse the meter leads for highest reading, or better 



still leave any one valve out oi 
remove the c.r.t. bast! connector 
to break the heater chain. 

Before leaving the subject of 
defective valves remember that an 
incorrect type or two transposed 
valves while not imposing any 
"cold" measurable short-circuit 
may take so much current when 
the set is switched on that it 
becomes equivalent to a heavy 
load. This can lead to a great 
deal of .time-consuming work, so 
always check that the right valves 
are in the right places in receivers 
that may have received unsuccess- 

attention. 

ing shorts in a printed-circuit model 



ful service 

When trac 

where the fault may He along one of several printed 
"leads" isolate each suspect in turn by cutting across 
the print with a sharp knife. If found free of fault, 
continuity can easily be restored by a small bridging 
blob of solder. 

Short-circuits that blow the fuse immediately on 
switching on are often due to the insulation of the 
older type of finned h.t. rectifier breaking down to 
the central mounting rod. Other possibilities are a 
defective double-pole mains on /off switch or the r.f. 
bypass capacitor shunted directly across the mains 
input. If this capacitor is found defective remember 
that the replacement must be of at least 500V and 
preferably 750V a.c. working voltage rating to with- 
stand the peak voltage inputs and surges. 

Replacing surge I i miters 

After replacing surge limiters which may have 
gone open-circuit through length of service it some- 
times appears that the set is taking excessive h.t. 
current, the replacement resistor running hot or even 
smoking. Most new wire-wound resistors give off a 
certain amount of smoke at first, and in most cases it 
will be found that the set is only taking normal cur- 
rent, but quite often the wattage of the replacement 
resistor is insufficient or the resistance excessive. 

The value of surge limiters is closely related to 
the value of the reservoir capacitor and the type of 
rectifier so that the correct value should be obtained 
from the relevant service manual rather than just 
fitting whatever low- value resistor is to hand. 
For example in many dual-standard KB/RGD 
receivers the tapped surge-limiter resistor has sections 
of SO, 170 and 19^ but all too often in service work 
we come across open-circuited sections in these and 
other receivers shunted by the widely used 250 or 
50^ resistor. This results in reduced h.t. and e.h.t. 
and although while the set is new it does, not have a 
very great effect it becomes very apparent in older 
receivers with tubes past their best. 

On the other hand of course nothing prejudices 
the life of a rectifier whether valve or silicon as much 
as reducing the value of surge limiters below the 
manufacturer's recommended figures. ■ 



309 




AERIAL 



A.J.WHITTAKER 



THIS month we shall describe the construction 
of a television aerial for Bands I and III. 
It may be used as a loft aerial or outside. 
The author has constructed this aerial system, com- 
prising a dipole with reflector for Band I and a 
Yagi for the reception of Band III. The two are 
linked by a twin-wire feeder the length of which 
is arranged so that on Band I it matches the dipole 
at about 750, the other end of the wire offering 
a high impedance to the Yagi which is tuned to 
Band III {by the length of the various elements). 
When the aerial receives a Band III transmission the 
feeder acts as a high impedance at both ends. 
Thus it is not necessary to employ a diplexer or 
filter unit. More about these in a later article. The 
aerial is located in the loft and a good signal is 
obtained from Tacolneston (Norwich), which has 
a vision frequency 56-75 MHz, the dipole being 
cut for a frequency of 55 MHz, and from the Band 
III transmitter at Mendlesham, which has a vision 
frequency of 204-75 MHz, the dipole here being 
cut for a frequency of 203 MHz. 

The Band I aerial rods are made from \ in. 
copper tube fastened by U -clamps to the wood 
boom. Figure I shows the constructional details. The 
length of the dipole is calculated from the formula 
468//, where / is the channel frequency in MHz, 
giving an answer in feet. This formula gives the 
length of the dipole taking into account the dif- 
ference in the velocity of electromagnetic waves 
travelling along a wire to those in free space (i.e. 
the velocity factor). The dipole is separated in 
the centre by about 1 in., but this is not critical. 
The Band III dipole, reflector and director 
elements are made of |in. copper tube fastened to 
the boom by U-clamps. The various lengths of the 
elements are worked out from the previously given 
formula. Bending the folded dipole may be. done 
by filling the tube with sand or by using a bending 
spring. The fold is best formed by bending around 
a 2 in. radius, a little help being given by judicious 
use of a blow lamp to soften the copper at the 
bend. The constructional details are given in Fig. 2. 



Adding a reflector to a dipole improves the for- 
ward gain by about 4 to 5 dB. Adding directors 
increases this by approximately £dB per element and 
also improves the bandwidth. These are typical 
figures which will vary- with the frequency and hence 
with the design of the aerial system. 

Fig. 2 also shows the method of fixing the ends 
of the dipole on the boom and the attachment 
of the feeder and connecting line. Lengths of the 
various elements for the Yagi aerial (channel II) are: 

R (reflector) length =A/2- 27-6 in. 

D (folded dipole) length— 27-6 in. 

Length of dipole end to end =55-2 in. 

/I (director) length = 0-43A = 24 in. 

12 (director) length = 23-5 in. 

/3 (director) length =23 in. 
The length of the twin feeder connecting the 
Band I and III aerials is 14 ft. (750 unscreened). 
The boom is of wood, length 60 in., cross-section 
3 by 1| in- 

TV AERIAL FEEDERS 

Concentric feeders are used to connect the aerial 
system to the receiver. A concentric feeder is one 
in which the centre conductor is entirely enclosed 
by the outer conductor which is a screening copper 



J?ef lector 



Saddles or U-clamps 
screwed to boom 



Wood boom 
55>"x 3*x 1 Uj 




Hole 

for 

feeder 



Twin 
feeder// 



Dipole 



Fig. 1: The Band I aerial comprises a dipoie plus reflector. 



310 




clamps 



boom 

wood 



Receh 



l$* '''Twin feeder to Band I dipole 
Fig. 2: Constructional details of the Band III Yagi aerial. 

braid covered by a plastic sheath, a practical example 
being the well-known coaxial cable. This may be 
single screened wire or twin screened, but the latter 
is seldom used nowadays for domestic installations. 
Fig. 3 shows a section of these feeders. 



Screen conductor Conductor 



Screen, Conductors 





Fig. 3: Single and twin screened coaxial cables. 

A transmission line is composed of inductance 
L and capacitance C per unit length all along the 
length of the wire (see Fig. 4). Matters must be 
so arranged that the reactive components L and C 
of the line cancel, so that the line becomes effectively 
a pure resistance. To bring about these conditions 
we must arrange that a certain value of load across 
the end of the line causes it to resonate. In this 
condition the L and C components cancel. 




Fig. 4: Equivalent circuit of a transmission line. 

It can be shown mathematically that \/LJC must 
be the value of the terminating resistance to produce 
the condition of resonance in the transmission line 
or feeder in order to make it into a line of pure 
resistance. The signal will then travel from the aerial to 
the receiver with the minimum of impedance. >J LjC 
for domestic coaxial feeder is typically 750, If 
we had a resistance of a very much smaller 
value than this at the receiver end the signal would 
be reflected and standing waves would be present 
on the feeder. A similar set of conditions occurs 



if the receiver end is of a higher 

resistance than s/LjC or is open- 
circuited. 

At the aerial end the system 
should be resistive at the frequency 
of the transmission and should 
remain so over a band of channels 
relating to the particular band for 
which the aerial system is designed. 

The effect of feeder mismatch is 
not terribly serious if the length 
is less than 100 ft. If the feeder is 
longer than this degrading of the 
picture quality may occur due to 
blurring of the image (i.e., the 
picture appears out of focus). As 
the length increases the effect of 
mismatch may cause ghosting 
(i.e. a ghost image appears to the 
right of the main image). 

For single-channel operation in Bands I and III 
aerials require a bandwidth of typically 5 MHz 
for the 405-line transmissions. Bandwidth require- 
ments of the u.h.f. channels are more critical. 
Individual u.h.f, channels are 8 MHz wide and the 
four channels allotted for each area will cover 
a total bandwidth of 88 MHz. The agreed variation 
in gain should not be greater than 3 cB over the 
band. Front-to-back pickup should be 16 dB with 
minimum side pickup. More about u.h.f, aerials 
next month. 

The characteristic or surge impedance of the con- 
centric feeder is given by the formula 138Iog6/a 
(see Fig. 5). This is typically 7511 but other 
impedances are available depending upon the design 
of the cable and the termination required. For 
instance a A/4 Marconi aerial would require a 
400 feeder. 

AH forms of dipole aerial are essentially balanced 
systems with respect to earth. Thus it is theoretically 
necessary for the feeder to be balanced m this way 
as well. The single core coaxial feeder is an 
unbalanced feeder because the screen is usually 
earthed at the receiver end. There are available 
balanced twin-core feeders but nowadays it is the 
practice to do the job the hard way and use single 
core feeders. The unbalanced cable works satisfac- 
torily when connected to a dipole or Yagi aerial 

Balun short-circuited to feeder screen here 

f 

b 

r , 




Fig. 5 {above left): Concentric feeder characteristics. 
Fig. 6 (below): Construction of a simple BALUN. 



311 



on Bands I and III (there seems to be some argu- 
ment and speculation about this problem amongst 
aerial manufacturers), but with colour television 
it may well prove essential for the feeder to be 
correctly balanced and terminated to avoid 
deterioration of picture quality. 

A device for balancing a coaxial feeder is known 
as a BALDN (from BALance to UN balance). This 
may be simply made up as shown in Fig. 6, using 
a quarter wavelength piece of copper tube. The 
i-wave matching tube presents a high impedance 
which prevents the waves from travelling over the 
surface. Its performance and bandwidth depend 
upon the frequency. 

ATTENUATORS 

In areas of high signal strength it may be neces- 
sary to attach some form of attenuator to the feeder 
to cut down the signal input to the receiver. This 
must not upset the feeder termination. Figure 7 
shows how this may be 
done. The simple T-net- 
work of resistances forms 
an attenuator for reduc- 
ing signal strength at the 
input terminals of the re- 
ceiver. If we assume 
the feeder to be 75ft, the 
aerial input at the receiver 
to be 75Q, and /V is the factor of attenuation, then 



R1 



Aerial 
feeder 

?sn 



Rl 

Wv\ — o 



Receiver 
75n 



Fig. 



7: Simple T-network 
attenuator. 



Rl 



and 



R2-75 



( 2N ) 

V(N+1)(N-1)/ 



If we wish to cut the signal down 20 times (i.e. 
201og 20=-26dB), then iV=20 so that 



68Q and 



R1 = 75 G9 = 

R2 = 75 (^i) =7 - 8!! - 



The resistors should be of the -J-watt, 10% high- 
stability type and selected from the standard values 
available. This will give Rl 6812 and R2 7-5Q. 

In conclusion one final note on the simple aerials 
used on Bands I and III. These are basically 
resonant-type aerials in that the optimum perform- 
ance is obtained at one frequency (i.e. the frequency 
of the transmitter the aerial is tuned to). The sub- 
ject of bandwidth arises when one considers how 
far away from this centre frequency one may 
deviate before an unacceptable degrading in per- 
formance takes place. Aerial bandwidth may be 
defined as that frequency range over which the 
impedance, gain and directivity fall off to an 
acceptable extent. 

TO BE CONTINUED 



SERVICING TV RECEIVERS 

— continued from page 303 

punctured. Other causes of non-operation are an 
open-circuited blue lead and a split solenoid, or 
merely that the moulded cam on the rear of the 
switch spindle is loose and is not rotating with the 
spindle to operate the S4 switch. 



*IV-R*OtO' ONLY 




Fig. 4: Right-hand side panel, 950 chassis, showing the 
position of the system switch solenoid. 

In the case of the semiportables, which use the 
" 960" chassis, the solenoid is on the left side and 
operates the push bar at an angle. With this system 
the solenoid may chatter continuously if the side 
lever is not engaging, A visual inspection will show 
this immediately although a description of the 
operation may not clarify what happens so easily. 

Checks for inoperative solenoids 

In short therefore if the solenoids are not work- 
ing check the supply to the tuner switch and make 
sure these contacts are being operated by the plastic 
cam. If there is no supply to this point, check 
RI47 which may be open. Note: if the cut-out is 
open (not the resistor), the set will not operate 
at all. If the supply is going through S4 correctly, 
check the leads to the solenoid and check the 
solenoids to make sure they are intact. 
CONTINUES NEXT MONTH 



312 




LTHE F 





®® 



MARTI 



A CONVENTIONAL oscilloscope is used to dis- 
play the relationship between two variables in 
the familiar graphic form. In most practical 
cases in the course of television servicing and experi- 
ments one of the variables is time marked out by the 
horizontal X-deflection of the spot on a c.r.t. screen 
and the second variable is the voltage waveform to 
be examined, marked out by the simultaneous verti- 
cal Y-deflection. 

The timebase for the X-deflection is normally 
traced with a suitable waveform derived from an 
internal sawtooth oscillator. Its waveform and the 
Y-deflection waveform to be examined are normally 
both periodic, possessing respective steady frequen- 
cies. Only if these respective frequencies bear a 
simple whole-number ratio relationship to each other 
is it possible to obtain a stationary display on the 
c.r.t. screen, because otherwise successive traces 
drawn during successive strokes of the timebase will 
not coincide in position on the screen. If the discrep- 
ancy is .only slight the display will appear to wander 
slowly, but if it is large we obtain a jumble covering 
the entire width of the display without being able to 
discern any waveform. 

In principle it would be possible to adjust the fine 
frequency control of the timebase until the display 
comes to a standstill, but this alone is not sufficient 
because it is too critical. We require some further 
device which forces a more positive lock, i.e. which 
gives a small range, not a mere point of the timebase 
fine control range, within which the display becomes 
stationary. This is effected by a process called syn- 
chronisation. We deliberately set the timebase oscil- 
lator running slightly too slow and then apply a 
portion of the Y-deflection voltage to give the time- 
base a jolt once each cycle, thus automatically speed- 
ing it up the correct amount to effect a rigid lock. 



This process is self -stabilising because the jolt auto- 
matically increases if the timebase gets more out of 
step, and vice versa, within reasonable limits. 

The foregoing brief discussion has made it clear 
that the basic oscilloscope requires a cathode-ray 
tube with power supplies, a sawtooth oscillator as 
timebase, a pair of high-level voltage amplifiers to 
produce the large voltages required at the c.r.t. elec- 
trodes in order to move the spot through adequate 
horizontal and vertical distances on the screen, and 
a synchronisation amplifier to apply suitably distorted 
fractions of the Y-deflection signal to lock the time- 
base into step. The oscilloscope described in the 
present article possesses all these features. 

PERIODIC WAVEFORMS 

The great majority of waveforms encountered in 
television work, and certainly all waveforms encoun- 
tered in receiver servicing, are periodic, i.e. they pos- 
sess fixed steady frequencies, usually the line or the 
field frequency of the particular television standard. 
The described synchronised free-running timebase is 
always satisfactory for displaying stationary pictures 
of such waveforms. 

It may become inconvenient if the waveform to be 
displayed consists of very sharp periodic pulses with 
nothing in between. The timebase must always run 
at the signal frequency or a sub-multiple thereof, 
because a harmonic of the signal frequency would 
produce multiple stationary traces, ultimately a com- 
plete raster as intended deliberately for displaying 
TV pictures. Thus for displaying a waveform on an 
oscilloscope with a synchronised timebase at least 
one period of the signal waveform must appear 
across the screen. Now if fh&signal waveform con- 
sists of only a very narrow pulse in each otherwise 
blank period clearly the synchronised timebase will 






TV 



313 




$ 




fjQ 

lb 




MV3 



MICHAELIS. M.A. 

inevitably give a very small and cramped trace of 
this pulse at one edge of the c.r.t. screen. In order 
to examine the pulse in greater detail we must mag- 
nify its display. This is possible only by using a 
different type of timebase which is not free running. 
It is triggered off to start a single run across the 
screen whenever a pulse arrives so that the speed of 
the run across the screen may be adjusted to any con- 
venient value to suit the duration of the pulse, irres- 
pective of the pulse repetition frequency. When the 
single run is finished the timebase flies back to the 
start and then waits until the arrival of the next sig- 
nal pulse fires it once again. 

TRIGGERED MODE 

In this triggered mode of operating a timebase syn- 
chronisation is obviously inherent because if the 
timebase starts one run coincident with the arrival of 
each signal pulse the successive traces must coincide 
in position on the c.r.t. screen. Furthermore it now 
does not matter if the signal pulses cease to arrive 
with a steady frequency but appear in arbitrarily 
fluctuating sequence. The display with a triggered 
timebase is still rigidly stationary whilst a synchro- 
nised timebase would be quite unable to resolve such 
non-periodic waveforms. 

In considering the design of the Videoscope MV3 
careful thought was given to the question whether 
or not to incorporate a triggered timebase function. 
The criterion is the extent to which such a function 
will be required in the course of work "with tele- 
vision equipment. Let us examine the problem 
from this angle. The only pulses of significance for 
servicing receipt tod CCTV equipment are the line- 
and field* p6lses;«lneir porches and the colour sync 
burst. All these are of adequate width in relation 
to the line or field period to permit the display of 




the necessary detail for servicing purposes using a 
synchronised timebase, and the latter is always usable 
because all these waveforms are periodic. For a wide 
range of ordinary TV design work and experiment- 
ing we may assume the same situation. 

On the other hand more exacting work and pro- 
fessional monitoring may well demand triggered 
displays. It may be necessary to examine pulse 
detail on test-pattern waveforms, or even to single- 
out test waveform lines transmitted by some stations 
between the field sync pulse and the start of the 
picture frame during normal transmission hours (for 
example this is common practice for networking 
purposes with the German Free Berlin TV micro- 
wave link to the German Federal Republic). Even 
these applications are still not concerned with non- 
periodic waveforms for which a triggered timebase 
is imperative. 

Non-periodic waveforms are rarely encountered in 
television work but there are some instances and 
these may even involve amateur work or the science 
education field. The most obvious example is the 
oscilloscopic display of pulses from Geiger counters 
and other types of detectors for nuclear radiation 
and X-rays. These pulses do have a statistical mean 
frequency but the sequence is always quite irregular 
and only a triggered timebase can give a stationary 
display. 

An important television raster principle often 
employed for examining nuclear radiation and X-rays 
is to cause each pulse to trigger a single timebase 
run at a vertical level on the c.r.t. screen cor res- 



314 



^ components list 














Capacitors: 


Resistors : 








C1 


39pFC 


R1 


9-1 MO 


R59 


470k ft 


R77 10kft1W 


C2 


12pF*C 


R2 


1-1MO 


R60 


100ft 


R78 8-2kft1W 


C3 


0-1 nF M500 


R3 


MMfl 


R61 


220k ft 


R79 120k ft Variable 


C4 


60|iF 1 25V E 


R4 


100 a 


R62 


220k ft 


R80 27k ft Resistors: 


C5 


1200pF C 


R5 


2-2Mft 


R63 


220 ft 


R81 120kft VR1 1kft lin. 


C6 


0-1 \lF M250 


R6 


680 ft 


R64 


1kft 


All 1 0% £W carbon VR2 2-5k ft lin. 


C7 


047fiF M250 


R7 


1 2k ft 1 W 


R65 


150ft 


unless otherwise VR3 5k ft lin. 


C8 


220pF C 


R8 


270 ft 


R66 


6'8kft 1W 


stated VR4 250k ft lin. 


C9 


150pF* C 


R9 


100ft 


R67 


4'7kft 1W 


VR5 100k ft lin. with 


C10 


01 [iF M500 


R10 


6-8kft 1W 


R68 


100ft 


d.p. mains switch 


C11 


1 ^F 350V E 


R11 


220 ft 


R69 


1Mft 


VR6 25k ft lin. 


C12 


O'VF M500 


R12 


100ft 


R70 


4-7kft 


VR7 250k ft lin. 


C13 


01 [xF M500 


R13 


100ft 


R71 


100k ft 


Valves: VR8 100k ft lin. 


C14 


25jiF 1 5V E 


R14 


2-2Mft 


R72 


1C 


Oft 1W" 


V1 EC92 VR9 1 k ft lin. 


C15 


1^F M100 


R15 


2-2MO 


R73 


5£ 


Oft 1W 


V2 EF184 VR10 2-5M ft lin. 


C16 


1 OOpF C 


R16 


100 ft 


R74 


1- 


5k ft 5W 


V3 ECC88 VR11 250k ft log. 


C17 


10pFC 


R17 


220 ft 






w.w. 


V4 ECC85 VR12 500 ft lin. 


C18 


22pF C 


R18 


220 ft 


R75 


6- 


8k ft 5W 


V5 ECC81 VR1 3 100k ft lin. 


C19 


0'047[iF M250 


R19 


4-7kft2W* 






W.W. 


V6 ECC85 VR1 , 8, 9, 1 2 and 1 3 


C20 


50^tF125VE 


R20 


2-2kft 1W 


R76 


A't 


f 0ft 1W 


V7 DG7-32 presets 


C21 


47pFC 


R21 


5'6kft 2W 










C22 


470pF C 


R22 


100ft 










C23 


4700pF C 


R23 


100ft 






Semiconductors : 


C24 


0-047 (iF M250 


R24 


5-6kft 2W 






D1 


250V p.i.v. silicon diode capacitance 


C25 


0-47ixF M250 


R25 


220k ft 








< 3pF 


C26 


10pFC 


R26 


270k ft 1W 






D2- 


D4 100V p.i.v. silicon diodes capacitance 


C27 


3pF* C 


R27 


51k ft 








< 3pF 


C28 


0-68txF M250 


R28 


100k ft 






D5 


100V, 500mW zener 


C29 


10pF C 


R29 


2-2Mft 






D6, 


D7 as D1 


C30 


1[*F M500 


R30 


100ft 






D8, 


D9 Silicon h.t. rectifiers, 0'5A, 1 kV p.i.v. 


C31 


002(iF M250 


R31 


120k ft 






D10 Silicon h.t. rectifier, 250mA, 1 kV p.i.v. 


C32 


560pF* C 


R32 


120k ft 






D11 


-D14 Silicon l.t. rectifiers or bridge unit, 


C33 


2000pF C 


R33 


2-2Mft 








60V a.c, 25mA 


C34 


470pF # C 


R34 


100ft 






D15 24V, 500mW zener 


C35 


0-1 t&F M500 


R35 


27k ft 1 W 






Tr1 


-Tr3 Silicon npn > 30V rating v/ith Is at 


C36 


2200pF C 


R36 


27k ft 1W 








least 20. BSY53, 2N1613, etc. 


C37 


0-047[iF 1kV paper 


R37 


470k ft 1 W 










C38 


0-22(iF M500 


R38 


120k ft 






Miscellaneous: 


C39 


1t*F M250 


R39 


120k ft 






F1 


1 A medium-delay 


C40 


8(iF 500V E 


R40 


1Mft 






LP1 


Miniature neon pilot lamp 


C41 


32 + 32|xF 500V EC 


R41 


51k ft 






PI 


Coaxial socket 


C42 


32 + 32(xF 500V EC 


R42 


33k ft 2W 






P2- 


P4 Shrouded banana sockets 


C43 


8|*F 500V E 


R43 


33k ft 1W 






P5 


3-pin mains plug 


C44 


50(xF 1 25V E 


R44 


10k ft 






RLY1 15k ft relay, 5mA snap-in, 2 changeover 


C45 


200|iF 35V E 


R45 


27k ft 








contacts (adapt any more sensitive relay 


C46 


33pF* C 


R46 


27k ft 








with appropriate shunt and series resistors) 


C47 


1SpF # C 


R47 


1Mft 






S1 


SPDT slide switch 






R48 


2-7kft 






S2 


2-pole 5-way rotary 


C = 


■ 500V ceramic 


R49 


47k ft 






S3 


1-pole 5-way rotary 


E = 


■ tubular electrolytic 


R50 


10k ft 






S4 


DPDT slide switch 


EC = 


= can-type electrolytic 


R51 


100k ft 






S5 


with VR5 


M = 


• microfoil or small paper 


. R52 


56k ft 1W 






T1 


Mains transformer. 350-0-350V 80mA, 




Following number is 


R53 


1Mft 








6-3V 0-5A, 6-3V 3A, 60V 10mA or nearest 




working voltage 


R54 


1Mft 








equivalent. Add 60V winding or 






R55 


82kft 






modify existing fourth winding or use 


TC1 


2-6pF 


R56 


820 ft 






small separate transformer (see text). 


TC2 


4-20pF 


R57 


100k ft 




Materia! for cabinet, fittings for c.r.t, printed 


Ceramic trimmers 


R58 


4-7kft 2W 




circuit board, wire, solder, etc. 








* see text 









ponding to the amplitude of the pulse. Many types 
of nuclear radiation detectors deliver pulses whose 
mean rate of arrival is proportional to the intensity 
of radiation and whose individual amplitudes are 



proportional to the photon energy (colour) of the 
radiation. It is thus clear that a triggered television 
raster produced from these pulses in the manner just 
described will possess bright bands at vertical levels 



315 



6dB bandwidth 2Hz — 5MHz 
(usable gain THz— 7MH2) 

A. 



Volts/centimetre valid with K>:i probe 
Max, sensitivity without probe lOOmV/cm 
Max. acceptable input 500 V pp with probe 



Sync 

amplifier 

Tr1,2,3 



Operative 2 Hz-6MHz sinewave 
Ramp 



Timebase 
»*» (grid base ramp 
oscillator) 
V4 




-y*K 



X- shirt 



Flyback 
blanking 



Coarse 

JL 



Speed 2£ 



Flyback pulses 



Fine 
25:1 
range 



(*> 



6dB bandwidth 2Hz-i*5MHz 

1 

Intensity 

Modulation 

amplifier 

V5 



Gain 






l...SOnS-2pS cm WiiS 

2...0*8-2OjjS cm ICOuS Full 5cm timebase 

3...S-200>jS cm TOOOuS > trace in slowest 

4...BO-2O00;jS cm IQOOOuS setting of fine 

5...0«8-20mS cm 100,Q00>isJ control 



Intensity 
modulation 

input 

Max. sensitivity IV pp 
for full drive of CRT grid 



® 




¥1 

Focus Intensity 



Max. horizontal 
sensitivity iv/cm 



Bright- up 

Blanking 



Trigger 
output 



Fig. 1: Block diagram with 
specification details of the 
MV3 Videoscope. 



corresponding to preferred photon emission energies 
in the studied radiation, and dark bands elsewhere. 
This effect is produced directly without any need for 
intensity modulation at the grid of the c.r.t. because 
the different brightness levels are produced by the 
relative probabilities of the timebase run falling at 
each level of the raster. This type of television raster 
is known as a spectrum raster, because the form and 
information content are identical to those of an 
optical spectrum produced from a visual light 
source with a glass prism. A spectrum raster display 
on an oscilloscope can be produced with quite simple 
circuits and thus constitutes a useful and interesting 
project for amateur experiments and scientific 
education. 

AUXILIARY MODULES 

It was decided to incorporate only a synchronised 
timebase in the Videoscope MV3 since this suffices 
for the great majority of ordinary television work and 
the reader not wishing to go beyond such work will 
welcome a basic oscilloscope of minimum complexity 
and cost. However it was fully appreciated that 
many readers will already require or will be enticed 
by the foregoing discussion to take up the more 
special kinds of experiments requiring a triggered 
timebase. The Videoscope MV3 has therefore been 
prepared so that the necessary auxiliary modules can 
be connected externally without modification of the 
basic instrument. A triggered timebase unit incor- 
porating a delay generator and another unit 



incorporating a detector for nuclear radiation and all 
auxiliary circuitry to display the spectrum raster are 
at present being designed specially for the Video- 
scope MV3. 

EXTRA FACILITIES 

In the present article we shall just outline the 
preparatory facilities incorporated in the Video- 
scope MV3 in order to be able to connect these and 
many other adapter units. These additions must 
be simple and as far as possible of general appeal 
for other purposes since otherwise it is unjust to 
burden the reader desiring only a basic instrument 
with their expense. Two facilities are actually 
needed. 

The first is a means for switching off the internal 
synchronised timebase and feeding any desired 
external signal to the horizontal deflection amplifier. 
This is a common feature of most modern oscillo- 
scopes and very useful for all manner of ordinary 
purposes such as phase and frequency comparisons 
of two voltage waveforms by way of Lissajous 
figures, display of magnetic hysteresis curves or any 
other examination of a function of two variables 
neither of which is time. To save components the 
same input socket and gain control serve for the 
sync amplifier and the external horizontal signal 
input, since the one is obviously never needed when 
the other is in use. 

The second facility required is a means for inten- 
sity modulation with an external signal applied to 




316 




317 



the c.r.t. grid after suitable amplification. This calls 
for a considerable number of components since it 
requires a third signal amplifier and a d.c. restorer 
and clamping system at the output for proper rela- 
tion to the static intensity control. Being an unusual 
feature for ordinary oscilloscopes it is necessary to 
justify its inclusion by further applications of general 
appeal. The obvious solution, and the one which has 
been taken, is to design the Videoscope MV3 so that 
it can be used to display ordinary TV pictures, e.g. as 
viewfinder for a CCTV camera. The necessary 
waveforms will be available from the camera with at 
most a few auxiliary components needed according 
to its particular circuitry. 

INTENSITY MODULATION 

Whenever a triggered timebase is used, irrespective 
of whether it is internal or external, it is necessary 
to use an intensity-modulation circuit because the 
spot will be waiting most of the time between trigger 
pulses and would burn the screen if not held cut 
off then. The static intensity control must be set 
beyond cut-off when using a triggered time base 
which generates the necessary bright- up pulses for 
the duration of each triggered stroke. Thus if the 
triggered time base adapter is an external unit we 
require external access to the c.r.t. grid via a suitable 
amplifier. 

FLY BACK BLANKING 

Apart from its necessity for triggered timebase 
operation and its usefulness for CCTV -viewfinder 
picture display, the intensity-modulation amplifier can 
also be used for flyback blanking and time spotting. 
Flyback blanking is desirable 'but not essential when 
using a synchronised timebase. Provided the time- 
base oscillator is designed so that the flyback is much 
faster than the forward stroke the flyback will leave 
a much fainter trace than the wanted forward stroke. 
This is because the trace brightness for a given beam 
voltage and current is always inversely proportional 
to the instantaneous writing speed. For the same 
reason an ordinary display of an accurate square- 
wave voltage shows faint flanks but bright roofs. 

When the forward stroke and flyback times become 
comparably long, and this is unavoidable at some 
of the higher speed settings in a simple circuit, the 
equally bright flyback trace can confuse the display 
by virtue of the resulting foldback. There is no 
distortion as such, so that if the flyback only can be 
blanked out by applying a suitable signal to the 
c.r.t. grid at the right times there is no objection 
at all to running a timebase oscillator under condi- 
tions where the flyback is sometimes as long as the 
forward stroke. 

Most simple timebase circuits do not deliver a 
sufficiently accurate squarewave pulse during the 
flyback of the sawtooth so that direct application 
of the distorted pulse actually present at some point 
of most customary timebase oscillator circuits will 
either blank or restore the trace too early or too 



late so that not all the flyback is blanked or part of 
the wanted trace is lost. Some pulse shaping is thus 
necessary and the easiest way is to overdrive an 
amplifier with the distorted waveform. Overdriv- 
ing any amplifier of sufficient gain with any arbitrary 
waveform always produces accurate square pulses. 
A. better way to convert any arbitrary waveform 
into a squarewave is to use a voltage-controlled 
bistable multivibrator known as a Schmitt triggei 
circuit, and this is the means adopted for the purpose 
in comprehensive professional oscilloscopes. But in 
the interests of the simplicity of our Videoscope 
MV3 it was decided to drive the intensity modulation 
amplifier heavily with the distorted blanking pulses 
from the timebase rather than to add still more com- 
ponents for a Schmitt trigger stage. Although this 
adopted solution does not give quite perfect flyback 
blanking at the highest speeds of all, it does give 
fully adequate blanking. Consequently it is per- 
missible to run the timebase right up to the point 
where the flyback is comparable to the forward 
stroke so that this design has been able to manage 
with fewer coarse ranges (thus a simpler switch) and 
broader fine ranges (greatly simplifying practical 
operation). 

DC RESTORATION AND CLAMPING 

Whenever intensity modulation is applied to a 
c.r.t. it is necessary to define the white and black 
potentials in a manner independent of the relative 
times spent by the actual waveform at these levels 
or in between them. If this is omitted the static 
intensity control of a TV receiver will have to be 
reset continuously according to the highlight-fo- 
shadow area ratio, or the static intensity control of 
an oscilloscope employing flyback blanking will have 
to be reset in conjunction with every change of time- 
base speed. 

The customary method of defining the black and 
white potentials in an unambiguous manner is to 
use a diode to clamp a particular level of the wave- 
form to the slider potential of the static intensity 
control. This is in effect a process of waveform 
rectification to obtain a d.c. voltage representing the 
correct mean brightness of the display and then add- 
ing this d.c. voltage and the waveform to the static 
brightness control potential. 

POLARITY 

Let us consider the required polarity of this pro- 
cess for the various applications of intensity modula- 
tion discussed in connection with the Videoscope 
MV3. For flyback blanking we desire the static 
intensity control to determine the trace brightness 
in a manner independent of the forward stroke to 
flyback ratio. Thus if we are going to apply nega- 
tive blanking pulses to the c.r.t. grid during flyback 
the blanking waveform must be clamped so that its 
positive intervals are at the potential of the slider of 
the static intensity control. We achieve this by 
coupling the waveform capacitively to the c.r.t, grid 



318 



Practical 

TELEVISION 



VIDEO AMPLIFIERS 

Video amplifiers are required to operate 
over a frequency range from d.c. to 6MHz. 
The problems involved in obtaining this wide 
bandwidth and the circuit techniques used 
are thoroughly surveyed. 



PROGRAMME PRODUCTION 

An account of the processes involved from 
the acceptance of an idea through to the 
final broadcast stage. 



FOCUS ON AGC 

In the return of the Focus series S. George 
describes modern a.g.c. techniques as 
found in hybrid receivers. 



UHF AERIALS 

The special problems of aerials for use at 
u.h.f. are outlined and details given of 
practical aerial systems. 

PLUS CHECKING AUDIO STAGES, 
POWER SUPPLY CIRCUIT AND CON- 
STRUCTIONAL DETAILS OF THE 
VIDEOSCOPE, AND ALL THE 
REGULAR FEATURES. 



ORDER YOUR COPY ON THE FORM BELOW 



(Name of Newsagent) 

Please reserve /deliver the MAY issue of 

PRACTICAL TELEVISION (3/-). on sate APRIL 

18th, and continue every month until further 

notice. 



NAME . . 
ADDRESS, 



.J 



to block any previous d.c. potential it may carry, and 
then connect a diode across the grid leak between the 
grid and the intensity control slider so that the 
cathode is at this slider potential. 

For time-spotting we require the same polarity. 
Time-spotting consists of marking the trace with 
equal intervals of time by feeding very narrow 
negative pulses of known frequency to the c.r.t. grid. 
This produces very short black gaps in the trace. 

This polarity of d.c. restoration is known as 
positive-limit clamping, or negative d.c. restoration. 
The converse, called negative-limit clamping or 
positive d.c. restoration, is appropriate J'or the b right- 
up function associated with operating a triggered 
timebase or displaying a TV picture. It is realised 
simply by reversing the diode. Evidently we must 
be able to connect the diode in either polarity at 
the grid of the c.r.t. in the Videoscope MV3. As 
the self-capacitance of a switch to effect this directly 
with a single diode would restrict the signal band- 
width unduly, remembering that we also desire to 
be able to handle television video waveforms, two 
diodes have been used with one end of each con- 
nected permanently to the c.r.t. grid. 

The switch is employed to connect the respectively 
required diode to the intensity control slider and 
the other one to the appropriate end of the intensity 
control track to hold it cut off. In this manner the 
very low barrier-layer capacitance of the diodes is 
always in series with the much larger switch capacit- 
ance so that the capacitive loading of the c.r.t. grid 
is essentially removed. 

This arrangement fulfils yet another vital function 
in that the diode not being used for clamping func- 
tions as limiter to prevent any dynamic excursion 
from exceeding the range of the static intensity 
control. Thus it is impossible to overdrive the c.r.t. 
by running it into grid current, a condition of 
operation expressly forbidden by the manufacturers. 

This completes our general discussion of oscillo- 
scope features required for television work and 
how these have been taken into account in the 
design of the Videoscope MV3. Apart from the 
special accessory units under preparation all standard 
universal accessories such as electronic switches for 
displaying two signals simultaneously may be con- 
nected to the Videoscope MV3 just as successfully 
as to any other oscilloscope. Next month we will 
commence with the circuit description and construc- 
tional details, including bandwidth and general per- 
formance considerations. Some years ago we 
published a first videoscope in this journal, and 
later some modifications, thus the present new design 
is the third generation and hence the designation 
MV3 in which the letters stand for the author and 
for videoscope. The present design essentially 
incorporates the same features as its nominal 
ancestors but with improved performance in keep- 
ing with further developments and in particular the 
need for a greater bandwidth which has arisen with 
the advent of colour television. 

CONTINUED NEXT MONTH 



319 



TELEUISI0I1 
RECEIVER 

TESTinC 

Port 10 by Gordon I. King 



It is noteworthy that the negative-going video 
modulation of the 625-line standard produces 
positive-going interference pulses, rising up in the 
same direction as the sync pulses themselves, and 
in the direct-sync system these can be mistaken for 
sync pulses, as shown in Fig. 1. Flywheet-sync 

■ Sync pulses ■ 

I 




FLYWHEEL-SYNC CIRCUITS 

GENERAL testing in the synchronising circuits 
was covered in Part 5 (October, 1968) and 
as was then promised this article deals essen- 
tially with tests in the more involved flywheel- 
controlled line circuits. Tests in this area have pur- 
posely been held over until now — subsequent to our 
dealing with ordinary sync and timebase testing — 
because flywheel-sync, as it is called for short, 
requires a different kind of line generator in most 
cases from that used in direct-sync systems, the 
sync, control and generator stages all being inte- 
grated, so to speak. 

Parts 5, 6 and 7 revealed that in direct-sync 
systems shaped pulses derived from the received 
sync signals are fed direct to the generators to 
trigger them at exactly the right instant for correct 
field and line locking. This sort of sync is always 
used in the field timebase, and there are still quite 
a few sets which employ it in the line timebase. 
However, in the line timebase it has the major short- 
coming that excessive noise carried by the line sync 
pulses, especially when the aerial is failing to yield 
a sufficiently strong signal and in areas of high 
impulsive interference, tends to trigger the line 
generator a very small fraction of a second before or 
after the firing point for optimum lock. This might 
not break up the lock completely but it can produce 
ragged vertical edges to the picture content due to 
the firing point hovering at random around the 
correct point. 

Fly wheel -sync is found in some quite early sets; 
but in these it was not always as successful as it 
should have been and this led some technicians to 
remove it in favour of the then more reliable direct- 
sync method. It subsequently lost favour with some 
manufacturers for a while, but with the advent of 
the dual-standard set (and colour sets) it came back 
again— this time more reliably! And now the vast 
majority of sets use it, either on both line standards 
or on 625 lines only. It will also be present in the 
latest breed of single-standard 625-line only models 
— monochrome and colour — so it is just as well to get 
some idea of how best to test it! 



mpuisive interference pulses 



Fig. 1: How interference pulses can rise in the direction of 
the sync pulses on 625 and disturb the sync performance. 

combats this in the line timebase, while in the field 
timebase — where the interference can cause vertical 
judder or rolling— special interference cancellation 
circuits are used; moreover, in the line timebase the 
disturbance is more noticeable on the 625 standard 
owing to the higher scanning speed and energy, 
which is why some dual-standard models run direct- 
sync on the 405 standard and flywheel -sync on the 
625 standard. 

The basic flywheel-sync scheme is shown in block 
schematic form in Fig. 2. Here the line sync pulses 
from the sync separator are fed via the differentiator 
network to a phase discriminator along with line 
pulses from the line timebase itself. The phase 



Line sync pulses 



Control potential 



input 
tram 
video 
amplifie 



Sync Sep. 

and pulse 

snaper 



Phase 
discriminator 



Electronic 
reactance 



Line 
timebase 



Fed -back Line pulses 



Fig. 2: Block diagram of the basic flywheel- controlled line 
sync system. 

discriminator is something like a discriminator type 
f.m. detector, in which the two signals it receives are 
compared one with the other in terms of frequency 
and phase. When the pulses are coincident in these 
characteristics the discriminator is balanced and it 
produces no control output. In this type of circuit 
the line timebase frequency is controlled by an 
electronic reactance connected in parallel with the 
frequency-sensitive elements (not uncommonly an 
ordinary tuned circuit composed of inductance and 
capacitance). The electronic reactance is often a 
valve arranged so that to the oscillatory signal it 
looks either like capacitive or inductive reactance— 
mostly the former — whose value can be altered 
simply by changing the grid bias. Thus since it is 
connected across the line generator the speed of the 
generator can be adjusted by varying the bias to the 
valve about a nominal standing value. 

The circuit is adjusted initially so that the line 
speed is correct when the discriminator is balanced— 
that is when the fed-back line pulses match those 



320 




Fig. 3: Flywheel sync circuit controlling a sinewave 

oscillator. Point "x" shows where a sync on/off switch 

can be connected. 

derived from the line sync pulses — and under this 
condition the picture locks linewise within the raster. 
Now should the frequency of the line generator tend 
to wander up or down from its correct frequency 
the discriminator will produce a plus or minus 
voltage which is fed to the electronic reactance in 
such :i manner as to correct the line frequency. 
Once the fed-back line pulses and the sync pulses 
coincide again in frequency and phase the discrimi- 
nator is brought back into the balanced state. 

This arrangement eliminates the ragged vertical 
edges to picture content and renders the set less 
sensitive to impulsive interference because the 
circuit feeding the control potential from the dis- 
criminator to ihe electronic reactance is relatively 
slow-operating. This means that it has a long time- 
constant and is thus unaffected by fast-occurring 




'Line pulses in 



Fig. 4: Flywheel sync circuit controlling a multivibrator line 
generator. The waveforms in Fig. 9 show the signals at 
the inputs to diodes D1 and D2 under balanced conditions. 



pulses of interference. Moreover, once an average 
value of control potential has been established a 
flywheel effect is achieved by the long time-constant; 
in fact in a well-designed and adjusted circuit it is 
possible for the generator to free-wheel in line lock 
for several lines if the line sync pulses happen to 
fail, which is certainly a feat that the direct-sync 
system is unable to perform. 

This type of flywheel circuit is shown in Fig. 3. 
where diodes Dl and D2 with the associated com- 
ponents form the discriminator, VI is the reactance 
valve and V2 the oscillator valve proper. The 
pentode valve is caused to oscillate at the frequency 
set by LI and Cl due to positive feedback from its 
screen grid to its control grid via C2 and Rl. The 
resulting signal is of sinewave form, but is shaped 
by C3 and R2 to a form suitable for driving the 
line output stage. 

SI is the standards change switch which when 
closed introduces C4 in parallel with Cl, thereby 
reducing the frequency of the oscillator. The switch 
is closed in the 405-line position, and since C4 is 
a preset the line speed can be set accurately for 
405-line lock after the line hold control itself (in 
the diode circuit) has been set for correct 625-line 
operation with SI open. 

It will be seen that VI is effectively in parallel 
with LI and its capacitor(s), and since this is the 
reactance valve the oscillator frequency can be 
made to vary by altering its grid bias, as already 
explained. The line hold control is connected 
across a voltage source and since its slider eventually 
feeds the grid of VI altering the control changes the 
grid bias and hence the generator frequency. This 
control is of course adjusted to establish the correct 
line lock when the circuit is receiving both sync and 
fed-back line pulses. If the frequency or phase of 
the fed-back pulses wanders a d.c. control output is 
produced by the discriminator diodes, and because 
this potential is directly communicated to the grid 
of VI the frequency/phase of the osciKator is modi- 
fied accordingly and is pulled back into step with 
the sync pulses. 

A slightly different arrangement is shown in 
Fig. 4. Here the generator is a multivibrator com- 
posed of V2 and V3, whose repetition frequency is 
governed to some extent by the time-constant of 
Cl in series with Rl, R2 and R3, R2 being adjust- 
able for line lock setting. In addition to the ordinary 
anode load resistor, the sync separator valve VI is 
loaded by inductor LI across which :he line sync 
pulses are developed and fed to the discriminator 
diodes Dl and D2. 

The discriminator also receives line pulses direct 
via C2 and as before accurate synchronising is 
achieved when the frequency and phase of the line 
pulses match those of the sync pulses. This is in 
effect because the potential at the junction of the 
two resistors across the two diodes is at a zero 
reference under synchronous conditions. In this 
circuit, when the frequency wanders from the sync 
pulse reference the resulting control potential is 



321 




Fig. 5: How incorrect flywheel sync phasing can displace 
the picture in the raster. 

fed to the grid of the first multivibrator valve V2 
via R4 and R5 instead of to a reactance valve. The 
overall effect is the same however because the 
change in potential at V2 grid changes the multi- 
vibrator frequency, increasing or decreasing it from 
that set by the hold control depending on whether 
the control potential is positive or negative — that is 
whether the generator is tending to run slow or fast. 
The circuit in Fig. 4 has separate line hold (lock) 
controls for the two standards, this being achieved 
simply by switching from one to the other on line 
change. There is also the added feature of the 




Fig. 6: In this example the phasing error, and hence the 
displacement is more severe. 

earlier is established by the components feeding the 
control potential to the reactance valve (Fig. 3) or 
the multivibrator (Fig. 4) and if these go wrong or 
change significantly in value unusual hunting effects 
will appear on the picture giving a sort of curvature 
effect to the verticals. 

However before we get too deeply involved with 
testing techniques it is instructive to consider one or 
two fault symptoms. It is possible with flywheel 
circuits for the repetition frequency of the generator 
to be matched with that of the line sync pulses yet 
the phase to be displaced by several degrees. When 




Fig. 7: The displacement here is to the extent of a cut-off 
on the left-hand side of the picture only. 

tuned circuit in the anode of the first multivibrator 
valve (V2). This rings at the appropriate line 
frequency (10,1 25Hz on 405 and 15,625Hz on 625), 
the correct ringing frequency being established by 
core tuning. On the 405 standard both inductors 
are in series, while on 625 the top one is switched 
out leaving only that connected nearest to the 
valve's anode in circuit. This ringing effect helps 
with the flywheel action. 

In both circuits the long time-constant referred to 




Fig. 8: Very slight phase error shows as part of the left- 
hand side oblongs being sliced off. Such an error can be 
caused by unbalance in the phase discriminator circuit. 

this happens the whole picture, while remaining in 
line lock, is displaced within the raster to the left or 
right, as shown by the photo in Fig. 5. An even more 
severe phase displacement is shown in Fig. 6, while 
much smaller displacements are shown in Figs. 7 
and 8. 

Some systems incorporate a special circuit for 
adjusting the phase of the oscillator independently of 
the frequency, and some of the early sincwave sys- 



322 



terns are of this kind. The idea is first to set the fre- 
quency for the best possible and most consistent line 
lock, irrespective of how the picture is displaced in 
the raster, and then adjust the phasing preset to bring 
the picture to the middle of the raster, avoiding the 
cut-off effect shown in Figs. 7 and 8. 

At this juncture the best way of adjusting the 
actual frequency must be emphasised. There is little 
point in swinging the line lock control over its range 
until the line pulls into lock, for it is possible to 
secure a temporary lock when the setting is far from 
accurate, and this soon shows up by the line flicking 
out of lock again on a change of scene or camera. 
The plan is to very carefully adjust the control until 
the picture continues to remain in lock or jump 
immediately into lock after pulling out the aerial 
plug and putting it back again. If this action neces- 
sitates resetting the lock control, then its original 
setting was wrong. To avoid having to test each 
time by removing and reinserting the aerial plug 
many sets feature a so-called push-and-twiddle con- 
trol (these are also present on the latest colour models 
—the BRC range, for instance) which is designed to 
disconnect the line sync input when pushed in. The 
rotating part of the control is the ordinary line lock, 
and once the sync has been disconnected by pushing 
the control in a very sensitive setting of this control 
is possible, the line just about locking (vaguely) when 
the setting is correct, at which point the knob is 
released to reconnect the sync thereby establishing a 
really solid lock which is unaffected by changes in 
picture content or interference and which occurs 
immediately the set warms up after a period of in- 
action. 





Fig. 9: Equal but opposite phase sync pulses are fed to 
the two flywheel sync discriminator diodes. 



Fig. 10: Hum in a flywheel-sync circuit. This is not 

uncommonly caused by a heater-cathode leak in an 

associated valve. 

If the picture phasing is in error after the correct 
locking position has been established the phasing 
preset (if fitted) should be adjusted to correct this, 
returning afterwards to the line lock to ensure that 
this is still optimised. If on the other hand it is 
impossible to lock the picture — albeit vaguely — and 
there is a tendency for the picture to come into lock 
when the control is turned hard in one direction, 
then the oscillator tuning must be corrected. When 
the circuit is like that in Fig. 3 the plan is to set the 
line hold control to range centre and adjust the oscil- 
lator tuning (the core in LI in this case) until the 
conditions as just mentioned are obtained. When 
the set has no means of line sync disconnection it 
sometimes pays to connect a simple toggle switch in 
series with the line sync pulse input to the discrimina- 
tor if this is possible (at the point marked X in Fig. 3). 

Sets without a preset phasing adjustment should 
automatically phase correctly when the generator 
frequency is set correctly. If this fails to happen, 
however, check any preset inductors present. If 
the picture remains well displaced within the 
raster it could mean that one of the discriminator 
diodes is faulty or even that one of the resistors or 
capacitors in the discriminator circuit is faulty. A 
fair degree of balance is essential for the circuit to 
work properly. Where a definite component fault 
exists the most likely culprit is one of the discrimina- 
tor diodes. 

Technicians or enthusiasts in possession of a 
reasonable oscilloscope can check the diode circuit 
for balance by monitoring the signals at the inputs 
of the two diodes and comparing the two displays. 
For correct working they should match each other 
closely, but will, of course, be of opposite phase as 
shown in Fig. 9, where (a) is the signal on one 
diode and (b) that on its partner. 

Circuits using reactance valves can cause quite a 
bit of trouble if the valve is a little faulty. For 
instance hum due to heater-cathode leakage can 
give the symptom shown in Fig. 10. 

NEXT MONTH: SOUND FAULTS 



L_ 




323 



A MONTHLY FEATURE FOR DX ENTHUSIASTS 



BECAUSE of the revised layout of the magazine 
the deadline for this issue has had to be 
brought forward so that only a short period 
can be reviewed, I was hoping that sufficient time 
would have elapsed for a significant improvement 
in DX to have taken place but alas the terrible 
conditions of the last period still persist. However 
there seems to have been at least some marginal 
improvement. 

Once again this is a combined report for M. Opie 
and myself of reception in the Bournemouth area 
for 13/1/69 to 31/1/69. SpE first: 

22/1/69 Czechoslovakia Rl. USSR Rl and East 
Germany E4. 

23/1/69 Czechoslovakia Rl. 

24/1/69 West Germany E2. 

25/1/69 Czechoslovakia Rl. 

26/1/69 West Germany E4. 

28/1/69 Czechoslovakia Rl. 

There was even one reasonably good day for the 
Trops on 25/1/69 with France F2, F8, F8a, F10 
and F12 all coming in quite well. This opening 
however, as is now usual, did not develop or last 
very long, and u.h.f. at this time was dud. 

Regarding F2 the USSR Forward Scatter Network 
in the 35-40 MHz band was once again active on the 
15th, 18th and 21st January, but for what exact 
reason is not yet apparent. 

Returning to the magnificent reception by F. 
Smales of Pontefract of WGR Buffalo Ch.A2, I have 
a letter from an old DX friend in the States, F. 
Dombrowski of Milwaukee. His local station relays 
WGR and I quote what he says: "During com- 
mercials for a WGR furniture store the huge letters 
WGR, are shown behind the announcer exactly as 
described in the January issue!" The operative word 
is huge; that I think explains why Frank could 
read them in spite of multi-path F2 images— other 
TV stations please copy! 

F. Dombrowski is an active member of an 
American club "The World-wide TV-FM-DX Asso- 
ciation", which as its title indicates is exclusively 
concerned with TV and f.m. DX. A monthly 
bulletin is published for interested DXers and the 
annual subscription here is 30s. ($3.50) by Inter- 
national Money Order. A specimen copy can be 
had for two International Reply Coupons (30 cents). 
Write to Mr. F. Dombrowski Junior. P.O. Box 5001, 
Harbor Station, Milwaukee, Wis. 53204. 

His general comments on DX this year in the 
Northern part of the States are of interest. For 
SpE he says 1968 was the worst ever for him, just 
like our experiences over here, but farther south 
things have been much better, as we recently 



CHARLES RAFAREL 

reported. The Trops were poor as well, with 
openings restricted to a maximum of 500 miles, 
whereas a year ago the distances were up to 700 
miles. Up to 1963 he logged 300 stations so his 
future scope is of necessity somewhat limited and 
he suggests that the future lies with u.h.f. DX. 

My sincere wish for DXers everywhere is that 1969 
will be better than 1968, So let us get ready now 
by overhauling the equipment. T have already 
started by fitting a new c.r.t. to the old Siera Belgian 
TV, extracting a couple of u.h.f. (now redundant) 
tuners, a c.r.t. over-run transformer and a mass of 
small components put in at various times for now 
obscure reasons! In fact I have nearly enough 
spares to make up another set! The old set is 
performing better than ever now that it has been 
returned to more or less the maker's original inten- 
tions; I suppose that under poor conditions one can 
get a bit too clever in trying to push up the gain, 

R. Bunney tells us that on Iceland TV there are 
now in addition to the original Band III station 
two low-power relays in Band I : Hvalfjordur Ch.E2, 
0.05kW; and Skalafell Ch.E4, 0.05kW. Although 
these are very low-power stations there is one 
advantage in that if an opening occurs over the 
Atlantic they are the only ones that could come in, 
so we might just be lucky. For the Test Card 
please see data sheet No. 23. 

I have been checking through O RTF's latest list 
of low-power relays for 1st chain, and I hope to 
give more news soon when a second list including 
u.h.f. is published. The list to hand covers North 
Eastern France and it is worth noting that Boulogne 
I Mt Lambert is operating on Ch.F4 horizontal at 
40W. I remember this one from a long time ago. 
It could prove a possible for DXers in the Dover/ 
Folkestone areas, as a " new" one. 

Since our report in the last issue of the very 
good log of Bruce Thomas of Castleford we have 
heard direct from him (the earlier information came 
from F. Smales). We now have the complete log 
for the Trop opening of 13/12/68 and in addition 
to the list we have already given he had Denmark 
Zeeland E6 and West Ju'dand E10 and West 
Germany Langenberg E9 in Band III. and on u.h.f. 
West Germany Dortmund Ch.25, Hamburg Ch.40 
and France Lille Ch.21. I make his total now 29 
stations in seven countries which is very commend- 
able indeed. 

D. Bowers of Saltash found some quite good SpE 
openings in December 1968 with Easr Germany E4, 
West Germany E4 (SWF and NDR), Czechoslovakia 
R2, USSR R2, Holland E4, Belgium E3, Spain E4, 
Norway E4, Sweden E4 and France F2 and F4. 



324 




G.R. WILDING 



Many BBC-2 faults that seem to be caused by 
u.h.f. tuner misalignment or a defective component 
switched in on 625 are due only to a faulty valve 
or to an over-advanced sensitivity control. For 
instance, we were recently called to see a Marconi- 
phone 23in. model which the owner said had intoler- 
able hum on BBC-2 but was all right on the other 
stations. The hum turned out to be vision buzz as 
anticipated but despite the most careful adjustment 
of the fine-tuning control it could not be eradicated. 

There was no separate u.h.f. sensitivity control for 
user adjustment so we switched off and examined the 
interior for a preset. The only sensitivity adjustment 
was a chassis-mounted local-distance potentiometer 
in operation on 405 only. On reference to the 
manual it Was suggested that if signal strength 
was sufficient to cause cross-modulation on 625 an 
aerial attenuator should be used. 

However although signal strength was adequate 
in this particular instance it wasn't excessive and of 
course the set had originally worked perfectly from 
the same aerial. There seemed a strong possibility 
therefore that some drift had occurred in the u.h.f. 
tuner. 

On switching on again BBC-2 reception was perfect 
but within a few minutes the vision buzz returned 
and gradually built up to an intolerable level. This 
was obviously caused by the effects of heat so we 
immediately replaced the PC86 r.f. amplifier and 
found that this completely cured the symptoms. The 
valve was probably passing some grid current when 
hot thus dampening the input circuit and altering 
the overall response curve. 

In another example after replacing an open -circuit 
mains dropper resistor in a modern Bush Model 
TV166U we found perfect v.h.f. reception but on 
u.h.f. the line hold was extremely edgy and the 
raster edges wavered about. 

The owner did not have a separate u.h.f. aerial 
but merely transferred the v.h.f. aerial to the u.h.f. 
input when required and thought the weak line hold 
on BBC-2 was due to not having the correct aerial. 
In point of fact the output from the v.h.f. aerial 
was more than adequate and on reducing u.h.f. 
contrast and slightly readjusting the push-button fine 



tuner the resolution of the finest gratings was out- 
standing, but the wavering and edg> line hold 
persisted although not to the same extent. We then 
replaced the PCF80 line oscillator and obtained 
perfect line lock. 

Finally we must mention that in some Thorn 
receivers (Ferguson, Marconiphone, Ultra, HMV) 
poor field hold on u.h.f. with normal field hold on 
v.h.f. has been due to a weak vision if. amplifier. 

On u.h.f. sync pulses occupy from 77% to 100% 
of carrier amplitude while on v.h.f. they rise from 
zero to 30%. Thus if a valve is slightly soft or has 
low emission the high amplitude u.h.f. sync pulses 
can be clipped or limited to impair their timebase 
triggering action. 

Timebase Squegging 

We had a very unusual fault in a modern Ultra 
19in. model recently. The complaint was normal 
sound, no picture, the latter being due to no e.h.t. 
Inspection showed both the line output pentode and 
boost diode to be without h.t. through an open- 
circuit fusible resistor. 

As there was no measurable h.t. short-circuit 
present we lightly resoldered the resistor clip and 
switched on. We then obtained wildly erratic line 
scans, some wide, some narrow and pulsating or 
oscillating about once per second. It was almost 
the timebase equivalent of a.f. motor-boating and 
if speaker hum level had been high or the set not 
so new we might have suspected an open-circuit 
main smoothing capacitor. 

Although not expecting it to cure the trouble we 
replaced both the 30FLI4 line oscillator and PL500 
line output pentode "just in case" (no matter how 
remote the possibility, it always pays to check- 
replace valves when investigating unusual faults 
before getting involved with circuit test;;). 

Results were exactly as before. We then put our 
meter test prod to the line output valve grid to check 
if line drive was similarly erratic and were immedi- 
ately rewarded with an almost normal if slightly 
smaller raster but which still pulsated slowly. On 
reducing the meter's voltage range the pulsations 
completely stopped, leaving a 
stable raster. Clearly the grid 
had been floating, that is not 
returned to the chassis till the 
meter was applied. 

In this particular model 
there were several suspects (see 
Fig. 1 ), a 470H grid stopper, %^~\J 
2'2Mfi grid leak and a v.d.r. p- — * £ 
or even the 1-8MH resistor 
leading to the slider of the 
width control potentiometer. 
All were really rather improb- 
able suspects since grid circuit 
resistors seldom go open- 
circuit. But the fact remained 



PL500 
Line 
I outpul 
valve Line 

\ , drive 



Boost 
HT rail. 



<S70 



0-047 



Fig. 1: Line output valve grid 
circuit. 




Pulse input rrom 
Line output trans. 



325 



that there was no continuity from the line output 
valve grid to chassis. 

We found the cause to be the v.d.r. becoming 
unsoldered from the printed panel. We often find 
high-wattage resistors becoming unsoldered from 
panels when subject to extreme overload, but in 
this instance as the set operated almost normally 
with the meter from grid pin to chassis and indicating 
a small negative voltage it was difficult to see why 
the v.d.r. had heated up. 

However, on resoldering the v.d.r. back into 
position, although we obtained an excellent raster, 
it started to heat up and we found that no less than 
500V developed across it. The only real possibility 
then was that the lQOpF 2kV capacitor feeding a 
pulse from the line output transformer to the v.d.r. 
was leaky. 

This proved to be the case, and on replacing this 
capacitor, and also the v.d.r. as it appeared to be 
somewhat damaged by the potential applied to it, we 
obtained a full size, perfect raster. 

Philips T-Vette 

One of these excellent 1 1 in. portables was 
brought in for service with the complaint of 
insufficient width on both systems. This receiver, 
similarly to other small portables, can be operated 
from the mains or a 12V battery, and our first move 
on plugging into the mains was to check the l.t. 
supply voltage. Normally it should be 11V, regu- 
lated by a three transistor plus zener diode arrange- 
ment so that despite mains voltage variations or 
the gradually falling voltage from a battery the 
l.t. rail voltage remains constant. 

The measured l.t. voltage in this receiver was 
only just over 9V, so lack of width was purely 
due to low l.t. In this model there is a preset 
potentiometer (supply adjust) which can vary the 
bias applied to a voltage-sensing transistor, asso- 
ciated with the zener diode, whose output in turn 
controls the base potential of another transistor 
emitter-coupled to an AD149 power transistor con- 
nected in series from l.t. +ve to the l.t. rail. The 
greater the forward bias applied to this last tran- 
sistor, as determined by the setting of the supply- 
adjust control or by a regulating voltage from the 
transistor/zener diode combination, the greater its 
conductance and the smaller the potential developed 
across it. Once the l.t. rail voltage is set at 1 1 V by 
the preset control variations in mains or battery 
supply are automatically compensated by the 
regulator circuit. 

To ensure that the receiver was not taking exces- 
sive l.t. current and thereby over-running the regu- 
lating circuit we removed the l.t. fuse and connected 
an ammeter across the clips to check consumption. 
Normally it should be 1-3A on v.h.f. and 1-5 A on 
u.h.f., but in our example it was just under 1A 
on both systems, so obviously the fault was in the 
l.t. supply system. 

Adjustment of the preset control had negligible 
effect on the rail voltage and although it varied 



the collector potential of the associated transistor, 
this seemed to produce no material voltage changes 
at the intermediary or power transistors. 

We then compared voltages with those in the 
service manual and immediately found a major dis- 
crepancy. The collector voltage of the intermediary 
transistor, termed the feedback amplifier, was over 
15V whereas it should be 5-25V on v.h.f. and 5-5V 
on u.h.f. The emitter of this transistor is directly 
and solely connected to the base of the power 
transistor or regulator. 

The resistors were all as specified so we next 
made the usual ohm checks from base to emitter 
and base to collector on both these transistors. 
However, the associated resistors were of so low 
value and the general circuitry such that the read- 
ings we obtained were meaningless and it became 
necessary to isolate them from the circuit. 

Always following the line of easiest checks first, 
we found that the big power AD 149 transistor was 
very accessible while the intermediary AC 128 was 
mounted on a small printed panel and its removal 
and replacement would entail delicate soldering. 

On removing the two base and emitter leads from 
the ADI49 we found a low base-emitter resistance 
with meter test-prods one way round but a high 
value when reversed— the normal results. 

However the base-collector junction was found 
to be open-circuit with the test-prods connected 
both ways, so obviously this transistor was the 
cause of the low l.t. 

With the power transistor's collector-base junc- 
tion open-circuit the receiver l.t. could only pass 
through a resistive network from supply to l.t. rail 
and there was no current path through the 
regulator. 

An excessive voltage drop therefore occurred 
across the latter thus reducing the rail voltage. The 
high intermediary transistor's collector voltage 
returned to normal when we replaced the AD 149, 
while the l.t. voltage rose to 1 1 8V which we could 
then reduce with the preset control. 

When testing transistors in this simple but quite 
reliable manner a reverse-forward resistance ratio 
of at least 25 : I should be found, but, of course, 
with high-power transistors the reverse resistance 
reading will be less than that for small-power types. 

Probably the two most useful attributes of a test- 
meter when servicing transistor receivers are an 
accurate low-range ohms scale and fine, sharp 
pointed prods. Resistor values can be so low that 
average ohms ranges will not indicate with certainty 
whether or not a short-circuit exists across them. This 
particularly applies to power supply and regulator 
circuits, where, as in this Philips model, resistors 
of 12, 10 and even 0*750 are employed. 

Finally, in all transistor service work check 
and recheck all possibilities to eliminate unnecessary 
transistor and component removal. In so many 
cases the greater proportion of time spent on tran- 
sistor TV service work is in replacing perfect items. 

TO BE CONTINUED 



326 



Indhh 



A CAPTION that should always be kept in 
readiness on BBC-2 is PLEASE DO NOT 
ADJUST YOUR RECEIVERS. Warnings of 
this type have long been useful to viewers on BBC-1 
and ITV's main and regional transmissions. They most 
frequently concern interference from foreign trans- 
mitters and other distortions beyond the control of 
the engineers of the studio or television transmitters 
concerned — or to faults in the GPO lines and links 
between them. Rarely are the station's engineers to 
be blamed. 

However quite a different situation has arisen on 
colour television, largely due to the amazing improve- 
ment in the colour quality of BBC-2 transmissions 
during the past few months. But this technical 
excellence is not consistently good and when BBC-2's 
colour is poor, oversaturated, distorted and out of 
alignment it is often so bad that viewers blame their 
sets and telephone their hire-maintenance service 
company demanding immediate service. Skilled 
television service engineers (with the right instru- 
ments) are worth their salt and added up all over 
the country can cost their employers hundreds of 
pounds in wasted time following for instance the 
transmission of poor colour film prints or video 
tapes or fourth -gene rati on duplicates of ghastly 
colour studio work. 

These nasty colours are mostly of foreign origin 
and are passable when seen in black-and-white. The 
American show Rowan and Martin's Laugh-In for 
instance is a crisp, slick and wisecracking show, and 
visually acceptable in black-and-white. In colour 
however the stars usually have faces as red as 
irascible lobsters (dipped in pyrosoda). Seen in 
colour the supporting cast resembles misaligned 
cartoon supplements in American newspapers. In 
the USA they don't seem to mind such distortion and 
viewers revel in the strange hippy trend of powerful 
chrornological hues that bear little relation to real 
life. 

The colour quality of the preceding BBC pro- 
gramme may have been excellent in every way: 
those programmes recently videotape recorded at the 
BBC Television Centre have benefited by the 
enormous strides which have been made not only 
in electronic equipment but through close collabora- 
tion in stage lighting and portraiture, make-up, decor 
and wardrobe. Together these contributions achieve 
an art which conceals art, a worthy objective. 

To reassure tenderfoot colour viewers, especially 
those with very new colour sets, the BBC should 
give advance notice of filmed or taped colour pro- 
grammes that are below par (as seen on monitors 



during rehearsal) as follows: THE COLOUR OF 
THE NEXT PROGRAMME IS BELOW 
STANDARD FOR REASONS BEYOND OUR 
CONTROL. PLEASE DON'T TWEAK YOUR 
SETS.' 

As we go to press I have just heard that BBC-2 
has made successful protests about the sour colour 
and some of the parochial Los Angeles jokes in the 
Laugh-In programme. 

RINGING THE CHANGES 

It will not be long before there will be three 
colour TV channels in operation in Britain, BBC-2 
plus BBC-1 and the fourteen Independent Television 
Companies. In some rather privileged '* high places " 
(on hills) it may be possible to pick up two or three 
different ITV channels in addition to the BBC colour 
transmissions. High outside aerials and low-loss 
downleads are usually necessary in any case, and in 
some sites it may be advantageous to twist the 
aerial on its mast by remote control towards the 
required signal. 

There may well be differences in colour balance 
between the ITV transmissions and those from the 
BBC. For everyone's sake it is hoped that all TV 
studios in Britain work to the same colour balance 
to ensure that the faces of the actors don't change 
from a ruddy sunburn on a BBC channel to an 
ashen pallor on a colour ITV station ! I have seen 
11 different styles of colour balance from II tele- 
vision stations on a hotel room receiver in America. 
Skin texture is the most important single common 
factor. The present BBC-2 colour test card (child 
and doll) is a splendid setting-up signal for all stations 
to use. 

WORLD MARKET FOR COLOUR AND MONOCHROME 

Transferring colour video tape to high-quality 
35mm. colour or monochrome film for the world 
market has been accomplished by Technicolor on their 
Vidtronios system shortly to be reported in Practical 
Television, and the different taste in colour by 
different nations can be dealt with in the colour 
grading of the film print required. The USA prefers 
a bold, warm, optimistic colour balance whereas 
Japan likes a much paler effect such as is readily 
obtained with shadowless fluorescent-tube studio 
lighting. The Continent of Europe seems to favour 
a low-key chiaroscuro of shadows, the taste be- 
coming more gloomy in Scandinavian countries. The 
lighting experts of the BBC colour television centre 
each have their own particular styles but all are 
nearer to my own particular liking for portraiture. 
This is soft low-contrast lighting which flatters even 
the most beautiful female face and emphasises the 
type of character to be portrayed. 

Strand Electric's "Cosmetic" lighting may help 
with this approach to theatre stage lighting too, 
which has suffered by the temporary abandonment 
of the most useful tool of the lot (when properly 
used), the footlights. The filler light is just as 
important as the keylight and the kicker light puts 
the emphasis in the right place just as imaginative 
colour separation between foreground actors and a 
busy backcloth can make the actors stand right out 
in a stereoscopic manner, 

BALLET IN COLOUR 

Ballet combines dancing with music, drama, mime, 
decor, wardrobe and colour. Dancing and music 






327 



are the controlling factors but colour influences 
every one of them. From the very start of public 
television in 1936 viewers have seen snatches of 
ballet in monochrome and, more recently, in colour. 
However good it was in black-and-white on 405 
lines, the transition of ballet to colour and to 
625 lines has made a tremendous advance. 

The transmission of The Sleeping Beauty from the 
stage of the Royal Opera House, Co vent Garden, 
beautifully performed by the Royal Ballet Company, 
was a delight for sore eyes. Antionette Sibley and 
Tony Dowell as Princess Aurora and Prince Flori- 
mand respectively were " backed " by a corps de 
ballet with delicately coloured dresses which looked 
charming in colour TV against magnificent scenery. 
Immaculately presented with superb lighting and 
valuable guidance by a pleasant young link man to 
introduce each act the whole lengthy programme was 
intensely satisfying. It had twice the impact of a 
monochrome picture. 

I look forward to colour outside broadcasts from 
another gracious London theatre the Coliseum, which 
has been restored to the original Matcham auditorium 
designs. Brilliant productions (in the English 
language) are now being presented there of new 
and recent operas in addition to long standing 
classics. Spectacular and dramatic productions 
include The Force of Destiny, a new version of 
Verdi's great work which includes big battle scenes, 
duels, choirs of 86 persons and field guns (with 
ammunition by Strand Electric) and brought from 
the audience at the opening night 19 curtains and a 
standing ovation. A pity it wasn't colour taped by 
the BBC. The magnificent lighting and technical 
knowhow of Charles Bristow and John Wyckham 
played an important part in the enormous success 
of Stephen Arlen's ambitious production. 

The delicate shades of colour in ballet and opera 
show up best when the three colour separations and 
their combinations are restored with consistent 
accuracy, such as is now achieved with the new 
Rank-Bush-Murphy and Plessey colour receiver inte- 
grated circuits. This development was first revealed 
by Bernard Rogers, Head of Bush TV Research, at 
the International Broadcasting Convention last 
October. Further details and a demonstration have 
just been given by him at a British Kinematograph, 
Sound and Television Society meeting. Described 
by many as a system which will take the worry out 
of set maintenance, it will soon be in demand by 
other set manufacturers. 

NEWS AND COLOUR 

So far I have been dealing this month with some 
of the better and finer things (and pious hopes) about 
colour television, to which I am now, needless to 
say, devoted. The newsreel cameramen at home 
and abroad have to make the best of any news story 
they can cover on colour motion-picture film. The 
newsreel cameraman is a pictorial journalist who 
has first to get his story, then to relate it (with or 
without sound) so that it can be cut together 
speedily, lending itself to commentary, when re- 
quired. Eastman Kodak or Gaevachrome are the 
film stocks mainly used for TV news coverage in 
Britain with 16mm, colour-reversal negative. 

With the widest variety of lighting conditions the 
news cameraman may film the laying of the founda- 
tion stone of a concrete monstrosity of a theatre 



building one day and be involved in militant student 
warfare on the next. How on earth is it possible 
to secure film that will cut together without startling 
colour balance changes? This is one ot the things 
to which Independent Television News attempted to 
find an answer when representatives of 14 FTV 
companies attended a conference in February. 

Under the Chairmanship of Cyril Moorhead of 
Independent Television News a common objective 
was sought as regards type of colour film stock, pro- 
cessing, magnetic striped sound usage, lighting, syn- 
chronising and still photo coverage. A tall order this, 
especially as comparisons with recent BBC achieve- 
ments have to be expected. There is a long queue 
of ITV orders for the Cintel flying-spot colour tele- 
cine, which includes the BBC's T.A.R.I.F. correc- 
tion device. The ITV companies each have their own 
individual ways of working in their local news 
operations and some of the best work in black-and- 
white has been networked from smaller regions such 
as Border and Westward. There are bound to be 
differences in style and proficiency but competition 
should keep them all on their toes. 

Certain rules for filming which date back to the 
days of Cecil M. Hepworth and orthochromatic film 
stock (which was insensitive to the colour red) and to 
portraiture still apply though we are now in the age 
of colour: (a) Try to film the face of your subject 
against a mid-tone background and not against the 
sky or a white background, (b) Expose for the 
shadows and let the high lights take care of them- 
selves, (c) Avoid profiles if possible, (d) Save 
footage. If your story can be joined together by 
merely removing the camera stops between shots 
you're doing fine, (e) Make sure the camera is steady 
and securely mounted. 

These are ancient rules. We must now add that 
quick pans, quick zooms, and gimmicky shots should 
be used sparingly; hand-held cameras do not have 
to shake; camera-film gates must be kept clean; and 
footage saved is useful — get the story with minimum 
footage or the film editor will have extra cutting 
to do. 

Television journalism concerns the film camera- 
man more than anyone else. He is a showman as 
well as a journalist and cameraman and must bring 
back the story in a showman-like way. I remember 
an occasion at Westward Television Plymouth when 
at 5.25 p.m. (17,25 to you) a cameraman drove in 
with his day's work. "A factory fire has just 
started on the other side of the railway bridge " he 
said handing in the film magazine of his day's work. 
"I'm going back to cover it." He was back at the 
factory within a minute of the fire brigade. Ten 
minutes later he was back at Westward with the 
story in another camera magazine — and the film 
processing department had the solution ready and 
warmed up for development. At 18.05 precisely 
the Westward News and Diary was on the air and 
behind the title was a sky-shot with smoke which 
panned downwards to firemen directing hoses on the 
seat of the fire — -a furniture store. More shots 
followed, all cutting together beautifully and com- 
mented on by the announcer. That's professional 
newsreel work, that is! 



J&7&4& 



328 



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SPECIFICATION: The Lawson range of new television tubes are designed to give superb 
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Complete tube fitting instructions 
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FOR YOUR INFORMATION 

Experience of supplying CRTs over 
many years has shown us that when a 
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14" Types 


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1 9" Types 


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21" Types 


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Carriage & Insurance 10/- 



PADGETTS RADIO STORE 

OLD TOWN HALL, LIVERSEDGE, YORKS 
Telephone: Cleckheaton 2866 
Indicator Unit Type 26. Size I2x9x9in. with outer case, fitted 
with 21in. C.R.T. type CV1526, 9 B7G valves, clean condition, 
but not tested. 32/6, P/p 10/-. 
New I2in. Speakers with built-in Tweeter, 3 ohm or 15 ohm — 

6 watt max, 28/6. Post paid. 

Indicator Unit Type 116A. Complete with VCR97 tube and 

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Speaker output. Transformer removed from TV. 3 ohm. 

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6in. Round, 3/-, P/p 3/-. 6 for 24/-, post paid. 

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Special Offer. Box of 50 new ARP12 valves 20/- post paid. 
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COLOUR 

TELEVISION 

SCHOOL 

DAYL1N ELECTRONICS ANNOUNCE A 

CORRESPONDENCE COURSE IN THE THEORY 

AND PRACTICE OF COLOUR TELEVISION 

A series of 10 lessons dealing in detail with: — 
Colour mixing, the PAL colour system, colour receivers, de- 
coders, IF circuits, time-bases, convergence, waveforms, set-up 
procedures, test equipment, fault finding, typical circuits. 
This course is designed for engineers who will be called upon 
to service colour television receivers within the corning months. 
Expert guidance throughout the course. Test questions with 
each lesson. Model answers supplied. Terms avai able. Certifi- 
cates awarded. 

Fee for the complete course 1 guinea;;. 

I 1 

To: DAYUN ELECTRONICS LIMITED 

32 PARKSTONE DRIVE 

SOUTH END-ON -SEA, ESSEX 
I Please send, without obligation, details of Your colour I 
| television course. 



NAME 



ADDRESS 



I 
I 

J 



329 




YOUR 

PROBLEMS 




PHILCO 1090 

I have put two new PCF80 valves in the tuner and 
the third one is now on its way out. I keep on having 
to retune the fine tuner every five or ten minutes. — 
L. Knibb (Northampton). 

We doubt if the PCF80 valves did fail. It is far 
more likely that a resistor has changed value. Par- 
ticularly check the 6-8kll oscillator anode load. 

SOBELL 7279 

There is no sound or vision on Channel 9, no sound 
on f.m. and a weak signal in the form of grey and 
black lines accompanied by a rushing sound on 
Channel 1. 

Channel 9 and f.m. failed first leaving me with just 
Channel 1 which was perfect for two months, then 
the picture suddenly began to go very bright, returned 
to normal for a few minutes then disappeared alto- 
gether. — J. James (Essex). 

The fault is due to a resistor in the tuner changing 
value or going o/c altogether. If you remove the 
tuner unit cover, you will see the resistor across the 
PCF80 valve base. The correct value of this com- 
ponent is lOkft 1W. 

GEC BT2748 

The above mentioned television set has given good 
service in the past. However after an evening's 
viewing on switching the set on the following day 
there was no sound, vision or raster. All the valves 
and the tube heaters were alight. 

There was complete lack of e.h.t. and the line 
whistle could not be obtained. — I. Sullivan 
(Middlesex). 

This is the symptom of voltage failure. Check 
on the h.t. line with a voltmeter. Zero voltage 
should lead to a check of the rectifier, fuse and 
a.c. feed to the rectifier. Low voltage could indicate 
a short or leak on the line due for instance to a 
failing electrolytic smoothing capacitor or an elec- 
trical leak in a transformer. 



Whilst we are always pleased to assist readers with their technical 
difficulties, we regret that we are unable to supply service data or 
provide instructions for modifying equipment. We cannot supply 
alternative details for constructional articles . which appear in these 
pages. WE CANNOT UNDERTAKE TO ANSWER QUERIES OVER 
THE TELEPHONE. The coupon from page 331 must he attached to 
a/1 Queries, and a stamped and addressed envelope must be enclosed. 



REGENTONE 194 

On switching on, the picture rolls upwards. After 
adjusting the vertical hold about three or four times, 
it remains steady. The PCL85 valve is in good 
order. — J. Hugo (Co. Durham). 

If the fault h not one of a weak field sync, check 
the resistors and capacitors associated with the hold 
control and pin 2 of the PCL85. 

PHILCO 1091 

Could you please state the correct resistor values 
for RIO and R14. They measured about lkft each 
but were marked brown black brown. I replaced 
these as I was looking for a fault i.e. no vision and 
no sound. I finally discovered there was no earth 
connection between the receiver panel and the time- 
base chassis. 

Connecting a wire to these restored vision and 
sound but there is vision-on-sound interference which 
has made me wonder if the above two resistors were 
correct after all. — J. Etherington (Surrey). 

Resistors RIO and R14 are both lkfi in value. 
The vision-on-sound may be due to excessive signal 
input or incorrect sound i.f. alignment. 

HMV 2633 

I am shortly moving from Manchester to an 
industrial area in Berkshire where piped BBC-2 is 
available. This comes on Channel 4 Band I. I 
would be grateful if you could tell me what modifica- 
tions will be necessary to enable my set to function 
on the above arrangements. — J. A. Somers (Berk- 
shire). 

The modifications are quite simple. Disconnect 
the lead from tag board connector E. Connect a 
shorting link between tags E and F. This allows the 
switching to take place whilst still maintaining the 
h.t. to the v.h.f. tuner. 

Replace the "U" biscuit in the v.h.f. tuner with 
the Channel 4 biscuit. 



330 



KB WV09 

Some months ago this set developed uncontrollable 
picture roll which was traced by a service engineer 
to an interelectrode short in the EF184. Shortly 
afterwards the picture lost detail on white and the 
picture depth decreased at top and bottom. There are 
also two faint white lines about half the picture depth 
apart, which slowly roll down the picture; Changing 
the PCL85 does not improve it. When either of the 
faint lines is in a position half way down the 
screen there is no appreciable difference in either 
half of the picture. I am wondering whether the 
trouble is in the interlace, and if so how to tackle 
it The picture is not sharply focused. 

Another trouble that developed after servicing 
was the picture came on after about half a minute 
as usual but was faint and takes about 20 minutes 
to attain full brilliance. There is plenty of 
brilliance then and the tube appears to be in good 
condition. — R. Bottomley (Somerset). 

Some of the loss of brilliance and focus may be 
due to the focus control changing value. It should 
be 2Mft. Check the 0-1 mF decoupling the boost 
supply to the height control, and the resistors 
lOOkn and IMa 

Check the electrolytic capacitors, especially that 
associated with the field output stage. 

BUSH TV75 

Although this set it fairly old the picture was 
a good one till I lost control over the brightness. 
On switching the set on with the brightness control 
fully down the picture comes on with too much 
brightness and the field flyback lines are visible. When 
the contrast is turned down the picture goes grey. 
All the valves are good so could this be a fault in 
the tube or the resistance network. — K. Hickman 
(Coventry). 

It is possible that there is a grid-to-cathode 
leakage in the tube. Quite often connecting pin 2 
directly to chassis with pin 11 connected to h.t. 
will clear the short. Check the brilliance network 
from pin 2 and the brilliance to chassis if necessary. 

KB KV001 

The trouble is vision on both ITV and BBC. It 
started about four weeks ago with a dark spot in 
the middle area of the screen. This could be 
removed by setting the contrast control full over 
to the left side and the brightness knob in a certain 
position. As time passed the picture took longer 
from cold to appear and over the period it grew 
worse until now there is no picture at all. — W, A. 
Lysamore (Devon). 

First listen for ithe line timebase whistle, If this 
is present check that e.h.t. is reaching the DY86 
(DY87) right side e.h.t. rectifier. 

If it is check this valve and the 2-7ft heater 
circuit resistor in the valve base socket. 



PYE 830A 

Occasionally I get a double picture with about 
one inch overlap. I can correct this by adjusting the 
vertical hold, but it doesn't stay put for long and is 
very critical. I have changed this pot and also the 
valves in the line section hut still no result. — W. E. 
Hicks (Birmingham). 

We advise you to check the PCL85 valve VI 3 for 
your trouble, and if this does not produce a cure 
check the 50m F electrolytic capacitor across one end 
of the small transistor sync panel mounted above the 
main chassis. This component may be given as 
C47 on your printed panel. 

KB 1192 

This receiver developed severe sound distortion. 
I have tested the PCL86 and this is in perfect work- 
ing order. 

I have also found on this set that the fine tuner 
tends to alter its setting but can be put right again 
with a quick twist of the channel changer. — K. L. 
Kirkley (Newcastle-upon-Tyne). 

Check the bias resistor of the PCL86 (I20O). Then 
check the 8-2Mft load resistor of the sound noise 
limiter diode (D7). Clean the turret contacts and 
ensure the valves have a good contact in their bases. 

PHILIPS 1768U-07 

The fault is that the line hold control will not 
correct line hold. By disconnecting the lead from 
the interference limiter control the fault is cured. 
What is the cause of this fault and its remedy?— J. 
Din (Bristol). 

Vision interference limiting on this model is 
achieved by making use of the suppressor grid of 
the video output valve. In your case the vision inter- 
ference limiter is tending to attenuate or distort the 
line sync pulses in the video stage prior to their 
application to the sync separator. The trouble lies 
in the limiting circuit so check the components in the 
video output valve suppressor grid circuit. 

EKCO 7418 

I am experiencing sound-on-vision on BBC- 1 
only. Could you also advise me as to the correct 
core to adjust to eliminate ringing. — E. Britton 
(Middlesex). 

Ringing accompanied by sound-on-vision inter- 
ference is symptomatic of misalignment of the 
vision i.L channel, possibly the sound rejectors. 
This adjustment cannot successfully be handled 
without the alignment instructions and suitable test 
equipment — signal generator and video output 
meter at least. Those skilled at the art however 
can often eliminate sound-on-vision by tuning for 
the best vision and then carefully adjusting the 
sound rejector in the vision i.f. strip for minimum 
sound on the picture; this though cannot generally 
be recommended. 



331 



PYE TV15 

The trouble started with loss of raster when the 
brightness control was turned up. In moving it to 
ray work room I dropped the set. After replacing 
the broken valves and making three repairs to the 
printed circuit I find that sound is satisfactory on 
both BBC-1 and ITV but can get no raster at all. 
The PCL84 video amplifier has been renewed while 
the PL36, PY800 and the EY87 have been tested and 
found all right. The usual tests for e.h.t. reveal bags 
of spark at the E ¥87 anode, but hardly anything at 
the tube. I have no means of reading the voltages 
obtainable. In passing I should mention that a DY86 
inserted in the EY87 bolder by mistake results in a 
clear picture but does not fill the tube width to its 
fullest. — J. Thompson (Lancashire). 

Our manual gives the e.h.t. rectifier VI 8 as a 
DY87. We advise you to try one of these in the 
holder before proceeding. 

The width controls R104 and R105 are on the top 
of the timebase panel, and other causes of low 
width are a defective PL36 or a leaky coupler 0-01 juP 
C87. 

SOBELL TP710 

There is a gap of about 2|in. each side of the pic- 
ture. Everything else is OK. — B. David (Aberdare). 

Check the line output valve and replace if neces- 
sary. Check the h.t. voltage and if this is lower 
than specified, change the h.t. rectifier. 



EKCO T433 

rhe picture has shrunk in size lin. top and bottom 
and lin. on the left side of the tube. I have had 
new valves (PY800, 30P19) but they have not made 
any difference. There is also a white line Jin. from 
the top of picture and 4in. long each side of picture. 
— H. Robinson (Lancashire). 

The reduced picture size should lead first to a 
check of the h.t. line voltage. If this is much below 
210V attention should be directed to the h.t. rectifier 
and, if you are sure thai this valve is in order, to the 
connections and components on its anode and 
cathode. If the voltage is about normal or a little 
high suspect low emission of the line output valve 
or booster diode. Also if necessary check the boost 
reservoir capacitor. When you have achieved the 
correct picture size, the lines — due to test pulses — 
at the top of the picture will probably disappear. 



I 
I 
I 
I 
I 
I 
I 
I 
I 

L 



QUERIES COUPON 

This coupon is available until April 18, 
1 969, and must accompany all Queries 
sent in accordance with the notice on 
page 329. 

PRACTICAL TELEVISION, APRIL 1969 



I 

I 
I 
I 
I 
I 
I 
-I 




77 



Each month we provide an interesting case of 
television servicing to exercise your ingenuity. 
These are not trick questions but are based on actual 
practical faults. 



^^ A Philips colour set Model G25K was said by 
£ its owner sometimes to give "green" pictures 
instead of pictures in full colour — yet at other 
times the picture was said to be perfect. Checking 
the set on Test Card F at the customer's home failed 
to reveal the symptom, the picture of a child with a 
blackboard being perfectly coloured in the centre 
circle. 

The main adjustments of the set were carefully 
checked, but no fault could be found. The set 
was then switched off and allowed to cool off, after 
which it was switched on again. Sure enough this 
time the coloured information in the Test Card 
had a greenish predominance. The switch-off, 
switch-on process was repeated and it was found 
that the picture was just as likely to appear " green " 
as in perfect hue. Exactly the same effect could be 
obtained by changing from a monochrome to a 



colour-encoded transmission and back again (mono- 
chrome always being normal however) or by dis- 
connecting and reconnecting the aerial alternately. 
What was the most likely cause of this symptom? 
See next month's Practical Television for a further 
item in the Test Case series. 

SOLUTION TO TEST CASE 76 
Page 283 (fast month) 

The Bush TV14I in last month's Test Case is 
the type with a line timebase stabilising device in 
the form of a voltage-dependent resistor (v.d.r.). 
This is connected to a tapping on the line output 
transformer and thus receives line pulses to which 
it gives a d.c. reference and hence a d.c. voltage 
across a load resistor in the line output valve control 
grid circuit. The d.c. voltage decreases when the 
load on the line output stage is high and increases 
when the load lightens, and in this way adjusts the 
stage bias to suit the load conditions — a sort of 
line output stage a.g.c. 

Examination around this section showed that the 
v.d.r. had failed in such a way that the grid bias 
was reduced on the line output valve, causing it 
to pass an excessive cathode current. This in fact 
was found to be almost 200mA against the normal 
140mA for a correctly operating and adjusted stage. 
The heavy current in the primary of the line output 
transformer caused its overheating and subsequent 
failure. 



332 



BOOKS BY G. A, BRIBES 

A QUARTER OF A MILLION COPIES 
HAVE BEEN SOLD SINCE 1948 



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Extract of letter from Mr. Wendell C. Ward, Texas, U.S.A. 

Sept., me 
I have recently read through Mr. Briggs' book 
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4 tor 28/-. 




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7/3 


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71- 


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a a 


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READERS RADIO 

85 TORQUAY GARDENS, REDBRIDGE, ILFORD, 
ESSEX. Tel. 01-550 7441 

Postage on 1 valve 3d. cirtra. On 2 valves or more, postage 8d. per 
valve extra. Any Farce] Insured against Damage ill Transit fid. extra. 



SAME DAY SERVICE 

NEW I TESTED! GUARANTEED! 



333 



MulKH&c 



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CED?a 



334 



Practical Television Classified Advertisements 

The pre-paid rate for classified advertisements is 4/- per line (minimum order 12/-), box number 1/- extra. 
Semi-display setting £2 10s. Od. per single column inch. All cheques, postal orders, etc., to be made 
payable to PRACTICAL TELEVISION and' crossed "Lloyds Bank Ltd." Treasury notes should always be 
sent registered post, Advertisements, together with remittance, should be sent to the Classified Advertisement 
Manager, PRACTICAL TELEVISION IPC Magazines Ltd., 15/17 Long Acre, London, WC2, for inser- 
tion in the next available issue. 



SERVICE SHEETS 



SERVICE SHEETS. Radio. T.V., 5.000 
models. List 1/6 S.A.E. enquiries. TEL- 
RAY. 11 Maudland Bank, Preston. 



BY 100s, 3/9 each; 3 for 10/-, with Free 
Surge Resistors, Lesmar. 15 Conholt Road. 
Andover, Hants. 



RADIO, TELEVISION over 3,000 models. 
JOHN GILBERT TELEVISION, lb 

Shepherds Bush Road, London W.6. 
SHE 8441. 



SERVICE SHEETS with Free Fault 
Finding Chart, 4/6d. S.A.E. Lesmar, 15 
Conholt Rd., Andover, Hants. (Mail only.) 

SERVICE SHEETS (1925-1969) for 
Televisions, Radios, Transistors, Tape 
Recorders, Record Players, etc., by return 
post, with Free Fault-Finding Guide, 
Prices from 1/-. Over 8,000 models 
available. Please send S.A.E. with all 
orders /enquiries, Hamilton Radio, 54 
London Road, Bexhill, Sussex. 



C. & A. 
SUPPLIERS 

SERVICE SHEETS 

(T.V., RADIO, 

TAPE RECORDERS, 

RECORD PLAYERS, 

TRANSISTORS, 

STEREOGRAMS, 

RADIOGRAMS) 

Only 5/- each, plus S.A.E. 

(Uncrossed P.O.'s please, returned 
if service sheets not available.) 

71 BEAUFORT PARK 
LONDON, N.W.11 

We have the largest supplies of 

Service Sheets (strictly by return 

of post). Please state make and 

model number/alternative. 

Mail order only. 

EDUCATIONAL 

TV and RADIO. A.M.I. E.R.E., City & 

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equipment) in all branches of Radio. TV, 
Electronics, etc.. write for 132-page Hand- 
book — FREE. Please state subject. 
BRITISH INSTITUTE OF ENGINEER- 
ING TECHNOLOGY (Dept. 172K), 
Aldermaston Court, Atdermaston, Berks. 



EDUCATIONAL 

(continued) 



BECOME "Technically Qualified" in your 
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(Dept. 858K), 148 Holborn, London, E.C.I 



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WITH ICS 



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WANTED 

DAMAGED AVO Meters, Models 7 and S. 
Also damaged Meggers, any quantity, send 
for packing instructions. HUGGETTS Ltd. 
2/4 Pawsons Road. West Croydon. 



WANTED 

(continued) 



SERVICE SHEETS purchased, HAMIL- 
TON RADIO, 54 London Road, Bexhill. 

WANTED— Popular Brand New Valves — 
R.H.S.. Stamford House, 538 Great Horton 
Road, Bradford 7. 

NEW VALVES WANTED. Popular TV 
and Radio types. Best CEsh price by return. 
DURHAM SUPPLIES, 367A Kensing- 
ton Street, Bradford 8, Yorkshire. 

WANTED new valves, television, radio- 
grams, transistors, etc. STAN WILLETTS 
37 High Street, West Bromwich, Staffs. 
Tel: WES 0186. 

£4 OFFERED for 64/65 Newnes Radio & 
T.V. Servicing. Small quantity of popular 
new T.V. valves wantec , give details and 
price please. BURTT, 93 Oldham Street, 
Warrington, Lanes. 

PHILIPS 19TG II 1A and Pye/Invicta 540 
moiorised Tuner Units. Box No. 72. 



WANTED. Vol. 5 of Television Servicing, 
Hawker & Reddihough. 1958-9 models. — 
TELE-S. 31 Cranbury Avenue, South- 
ampton. 

WANTED— Radio and T.V, Servicing, all 
volumes, 93 Keighley Road, Cowling, 
Keighley, Yorks. 

GOOD PRICE offered for Newnes T.V. 
Servicing, Vols. 59/60, 60/61, 61/62, 62/63 
and 63/64. Box No 73. 

NEW VALVES WANTED— any quantity. 
Good Service TV Ltd., 75 School Street, 
Wolverhampton. 26630. 

FOR SALE 

VALVE CARTONS at keen prices. Send 
1/- for sample and list. J. &. A. BOX- 
MAKERS, 75a Godwin Street, Bradford I . 

TOP TRADE DISCOUNTS FOR 

All 

COMPONENTS 
VALVES 
TUBES 

TRANSISTORS 

L.O.P.T's 

Free Trade Catalogue 

Engineers & Service Dealers Only 

WILLOW VALE, 

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WHOLESALERS, 

4 The Broadway, Hanwell, 

London, W.7 

01-567 5400/2971 



335 



MISCELLANEOUS 



CONVERT ANY T.V. Into an Oscilloscope. 
Instructions £1. REDMOND, P.O. Box 
38397, Los Angeles, California 90038. 



UFO DETECTOR CIRCUITS, data, 10s. 
(refundable). Paraphysical Laboratory 
(UFO Observatory). Downton, Wilts. 

PERMANENT BINDING— Have your 

copies of Practical Television permanently 
bound in black book-cloth. Title, volume, 
year, gold-foil blocked on spine. Price 35/- 
including postage. For special materials and 
finish — prices on application. Forward 
remittance and complete volume to: I. W. 
HANSON, 19, Gay Bowers, Fryerns 
Estate, Basildon, Essex. 



AERIALS 



TV AERIALS 



£1 IS 

£1 10 

£1 15 

CI 10 

£2 18 



Bind I. H. Mast Fitting 

Band 111, S Ele Mast Fitting . . 

Band l/|||. S/D and 4-Array . . 

Band IV. 10 Ele Array 

Band IV. IB Ele Array 

Lathing Kits from 10/-: Poles, Co-ax 9d,, Grade 

"A" ife. Plugs 7d. 

P. A P. 7/6. C.W.O.. S.A.E, for list. 

TELEI INDUSTRIES LTD. 
BREAKS PEAR ROAD, RUISLIP, Middx. 



SETS & COMPONENTS 



BOB'S BARGAINS. 10 assorted your 
choice 14/6. 100 assorted £5-10-0. PC F80 
PCC84 PL8I PL36 PY81 PCL82 PCL83 
EF85 U191 U301 30F5 30P12 PY33 
PY32 PY82 EB91 ECL80 ECC82 EBF80 
EBF89 6BW7. The following valves only 
at 12/6 per doz. EF80 EY86. AH valves 
tested. 3 BY100 type rec. with surge res. 
9/- p. & p. 6d, New 25k ohm w.w. controls 
2/- p. & p. 6d. EKCO U25 type plastic 
l.o.p.t. housings 12/6 p. &. p. 2/-. 
Mail Order Only. 2 St. James St., 
Rawtenstail, Rossendale, Lanes. 



TH/S MONTH'S SCOOP/ 

CRM 141, CAM 142, CRM 153 

NEW BOXED MAZDA 

57, 6 d. (Carr. & ins. 12/6d) 

TELEVISION TUBE SHOP 

48 Battersea Bridge Road, S.W.1 1 



VALVE BARGAINS 

ANY 5—9/-, 10—14/-. 100— £5 10s. 

FROM THE LIST BELOW 

ECC82, ECC83, ECL80, EF80, EBF89- 

EF91, EB91, EF85, EF184, EF183- 

EY86, PCC84, PCF80, PCL82, PCL83- 

PCL84, PL36, PL81, PL82, PL83, 

PY32, PY33, PY81, PY82, PY800, 

30PL14, U26, U191, 6-30L2, 30FL1, 

30P4, 3GP12, 30PL1, 30F5, 20L1, 
10F1, 20D1. 

P, & P. 1/-. 

MANY OTHER TYPES OF TV VALVES 
IN STOCK. 

3 BY100 TYPE RECTIFIERS 10/- 

VELCO ELECTRONICS 

62 Bridge St., Ramsbottom, via Bury, 
Lanes. 



SETS & COMPONENTS 

(continued) 

TELEVISION TUBE SHOP 

ALL THE LATEST NEW TUBES 
AT REDUCED PRICES 

A28-I4W .., £11. 0.0 

A47-HVV £19.19.6 

A47-I3W £11.15.0 

A47-I4W £7.12.6 

AS9-IIW £12.19.6 

A59-I3W £14.15.0 

A59-I5W £9.10.0 

A59-I6W £14.15.0 

AW2I-II £10.10.0 

AW36-20, 21 £5.12,6 

AW36-80 £5. 7.6 

AW43-80 £6. 7.6 

A W43-88. 43-89 £6. 1 2.6 

AW47-90, 91 £7.10.0 

AW53-80 £8.12.6 

AW53-88, 53-89 £8. 5.0 

AW59-90, 59-9 1 £8. 1 5.0 

CI7BM, FM, HM £6. 7.6 

CI7LM, PM, SM £6.12.6 

C2IHM, SM.TM £7.17.6 

CME 1201 £12.10.0 

CMEI60I , £10. 5.0 

CMEI702, 1703 £6.12.6 

CMEI705 £7. 7.0 

CMEI90I, 1903 £7.10.0 

CME2I0I,2I04 £8. 5.0 

CME230I, 2302 £8.15.0 

CME2306..,,.., £14.15.0 

CRM93.. £5.10.0 

CRMI24 £5.10.0 

CRMI4I.2, 3,4 is. 2.6 

CRMI71,2, 3 £6.7.6 

CRM2M.2I2 £8.17.6 

MW36-24, 44 £5. 2.6 

MW43-64, 69 £6. 7.6 

MW43-80 £6. 7.6 

MW53-20 £8,17.6 

MW53-80 £8.17.6 

7405A £6.12.6 

TSD2I7.282 £11.10.0 

All tubes tested before despatch and 

guaranteed for 1 2 months. 

Re-processed tubes also available at 

reduced prices. 

CARRIAGE 10/-, via B.R.S. or 15/- via 
passenger train. Add 2/6 for Compre- 
hensive insurance. 

Midland Stockists: — 
Amateur Electronics, 
5 1 8/520 Alum Rock Road, 
Birmingham 8 

TELEVISION TUBE SHOP 

48 BATTERSEA BRIDGE ROAD 
LONDON, S.W.I I. BAT 6859 

WE GIVE GREEN SHIELD 
STAMPS 



SETS & COMPONENTS 

(continued) 

R&RRADIO 

5 1 Burnley Road, Rawtenstail 

Rossendale, Lanes 

Tel. : Rossendale 3 1 52 

VALVES BOXED, TESTED & 
GUARANTEED 



E8C4I 


4/6 


PCCS4 


17- 


PYB2 


V- 


EBFS0 


3/- 


PCF80 


i- 


UI9I 


4/6 


EBF89 


3/6 


PCF82 


3/6 


6F23 


it- 


SCC82 


3/- 


PCL82 


«r 


30FS 


2/6 


:CC83 


41- 


PCL83 


41- 


30LI5 


31- 


SCL80 


3/- 


PCL64 


31- 


30PI2 


4/6 


EF80 


1/4 


PL36 


51- 


30CIS 


5r- 


= F85 


3/- 


PL8I 


41- 


30PLI3 


5/6 


•FI63 


3/6 


PL82 


4/6 


30PLI4 


5/6 


EY86 


41- 


PLB3 


41- 


S0CD6 


7/6 


EL4I 


31- 


PY33 


5/- 






EZ40 


4/6 


PY8I 

PY800 


J/6 

3/6 






POST ONE VALVE 9< 


. TWO TO SIX 6d. 




OVER SIX POST PAID. 





TOWER BY LTD 

For Line Outputs and Deflector Coils 
We have the Country's largest stock of Manu- 
facturer's Original (or Authorised Replacement) 
Line Output Transformers for many "difficult" 
makes, including Ambassador, Baird, Cossor, 
Decca, Oy natron, Ekeo, Ferguson, G.E.C., 
M.M.V., K.B., Masteradio, Peto-Scott, 
Philips, Regcntone, RGD, Soball, Ultra, 
etc. Also deflector coils output and oscillator 
transformers, inc. Alba, Bush, Murphy. 
Examples. L.O.P.T. Murphy 310/350/410/540/ 
659/759, 117/-; Bush TV60 117/-. TV22 & 24, 
78/6; Cossor 9S0 77/6: Ferguson 306/308 79/6; 
Philips 1768U L.O.P.T. assembly 122/6; Ultra 
1984-200c 101/3. 
Rewind most L.O.P.T, 90/-. 

SPECIAL OFFER 
Ekco improved type for Models T221, 231, 310 
all at 45 -; Ferranti 14T4 series inserts 25/-; 
Phi I co 1019/1021 52/6. Terms: C.W.O. or 
C.O.D. {3/6) post/packing 6/-; 2 or more 
L.O.P.T.s post/packing free. 
All enquiries answered but regret no lists 
available. Same day delivery on most types. 

TOWERBY LTD 

MAIL ORDER DIVISION OF T.C.S. LTD. 
70 STREATHAM HILL, LONDON, SW2. 

Tel: 01-674 2185. 



QUALITY NEW VALVES 

Orders value £2 or more— leas 5%. 



DY86 


6/3 


EZ80 


4/3 


PFL200 


18/9 


BOC82 


57- 


EZS1 


4/9 


FL36 


10/- 


ECC83 


5/3 


FC8S 


10/3 


FL81 


9/~ 


ECLSO 


e/s 


PC88 


10/3 


FL84 


6/9 


ECL82 


8<6 


FC97 


67- 


PL500 


13 9 


EF8S 


e/s 


FCC84 


7/8 


PY82 


5/8 


EF86 


6/6 


FCF80 


6'- 


PY83 


89 


EF1S4 


0/3 


PCL82 


7/3 


PY800 


71- 


ELS 4 


4/e 


PCLS3 


10/- 


PY801 


7/- 


EY51 


7/6 


PCL85 


8/3 


30F19 


13/6 


EY86 


6/9 


PCL88 


8/6 


30PL13 


18/6 




VALVE 


OFFER 




Minimum ill — your selection — do discount 


EB91 


Wh 


PCCI89 


8/9 


PY88 


8/6 


BF80 


4'S 


PCF8G 


87- 


V2S 


Wit 


EF89 


4/8 


PCF801 


7/- 


UCL83 


8/9 


EF183 


57- 


PCL84 


•}!- 


6A96 


i/n 


PCC89 


8 9 


FY81 


S/3 


30LI5 


12/3 



All valves guaranteed six months, Orders 6/— aod 
over post paid — under add 3d. Full lists component 
on request. 

J. R. HARTLEY (T3) 

78B High Street, Bridgnorth, 
Shropshire. 

(continued overleaf) 



336 



SETS & COMPONENTS {continued} 



TELEVISION TUBES 

Large stocks of television rubes, London's leading wholesale suppliers, all tubes complete with guarantee card. By return despatch. 
Terms: Cash with order, s.a.e. ail enquiries. 

14m. types. AW36/20, AW36/21, AW36/80, MW36/24, CRM141, CRM144, CME1402 etc £4 17 6 

17in. types. MW43/80, AW43/80, CRM173, CME1702, MW43/69, CRM172, AW43/88, AW43/69, CME1703, 

CME1705 etc . £4 17 6 

19in. types. AW47/90, AW47/91, CME1901, CME1903, CME1902, C19AH £419 6 

21 in. types. AW53/88, AW53/89, CME2101, CME2303 £6 12 

MW53/80, AW53/80, MW53/20, CRM211/2 £8 18 10 

23in. types. AW59/90, AW59/91, CME2301, CME2303 £6 12 

23in. Twin Panel. CME2306, A59-16W £13 1 

23in, Panorama. A59/11W etc £12 

19in. Twin Panel. A47-13W, CME1 906 etc £10 1 

19in. Panorama. A47/11W etc £9 

We stock all types of tubes. Carriage and Packing 12/6d. per British Road Services. Large stocks of valves, transistors, components, 

L.O.P.T's. Electrolube, Servisol switch cleaner, Multicore solder. Service Tools. 

WILLOW VALE ELECTRONICS LTD. 

The Service Dept. Wholesalers, 4, The Broadway, Hanwell, London. W.7. Teh 01-567 2971/5400 

FREE CATALOGUE— TRADE ONLY. S.A.E. Please. 



EX N.E.V. C.C.T.V. Camera and Monitor 
Circuits, S.A.E. for list, LOWE, 35 Hensiey 
Point, Hackney, London, E.9, 



BYIMTYPE 6 for 10/- 
5UPER SILICON RECTIFIERS 

TV etc., 1200 PIV, 800 MA 5/- or complete 
with instructions, resistor, condenser 6/6, 
400 PIV. HW 6 imp 6/-. 200 PIV.HW 6 amp 
6/-. CONTACT COOLED, I4RAI282/FC10I 
7/6, l8RD228l/rC124FW 13/6, EC I 12/6, 
EC2 12/6, 30v. 250mA FW 7/6, 2S0v. 
IQOrnA FW Grundig 12/6, FC1 16 7/6 
FIN Types. 

Equivs. for RM4 7/6, 14A97 13/6, I4A86 7/6, 
MAI 00 10/6, RM3 3/-. 

FW 12 volt I A 5/-, 2A 7/-, 4 amp 10/6. 
CHARGER TRANSFORMER 4 amp 12/6/2 
vok2l/6. Plus 3/- P. & P. 
LINE O.P.. TRANS: All 30/- each. 
Cossor 948, KB Queen, Peto Scoet 1920, 
1726, 1729, 1730, Murphy V3S0 and V230, 
Philips I446U/4S and I746U/4S with EYSI. 
MULTIMETERS from 32/-. 
Stamped envelope for full latest selection 
and bargain offers in CHEAP METERS, 
RADIOS, BABY ALARMS. INTER- 
COMS, WALKIE-TALKIES, SINCLAIR 
& EAGLE. Under £1 P. & P. 6d„ £1 to £3 
l/6d. No C.O.D. 

MAIL ORDER ONLY 

DURHAM SUPPLIES 

367A KENSINGTON ST., BRADFORD 8, TORKS. 



BAKER & BAINES 
Examples of prices: — 
BBC dipoie 30/-, X 38/-. H 42/-, 
ITA 5 ele 34/-, 8 ele 47/6, 1 1 ele 57/6, 
Combined BBC/ITA 1+5 45/-, 
H+5 69/-, BBC 2 8 ele 29/-, 14 ele 

37/-, 22 ele 63/-. 

All types generally available — prices 

include mounting clamps and postage, 

11 Dale Crescent, New Tupton, 

Chesterfield. 



BARGAIN PARCELS 

10_13/-, 20—24/-, 100— £5 FROM 
THE FOLLOWING LIST:— 

ECC82, ECL80, EBF89, EF80, EF85, 
EF91, EB91, EY86, PCC84, PCF80, 
PCL82, PCL83, PL36, PL81, PL82, 
D L83, PY33, PY81, PY82, 6-30L2, 
30FL1,30F5, 10F1. 

S. ASHWORTH 

9 MANDEVILLE TERRACE, 

HAWKSHAW, VIA BURY, LANCS, 



150 NEW ASSORTED Capacitors, Re- 
sistors, Silvered Mica, Ceramic, eic. 
Carbon, Hystab, Vitreous £-20 watt, 12/6, 
Post Free, WHITS AM ELECTRICAL, 33 
Drayton Green Road, West Ealing, 
London, W.13. 



WITWORTH 
TRANSFORMERS LTD. 

Dept. P.T.. 26 All Saints Road, 
North Kensington, W.I I 

Telephone: 01-229 9071. 9 a.m. till 5 p.m. 

TELEVISION LINE 

OUTPUT 

TRANSFORMERS 

PRACTICALLY ANY MAKE OR MODEL 
SUPPLIED OK REWOUND 

EKCO, FERRANTI, DYNATRON 

Replacement cases 16/- each, please state 
model. 

S.A.E, for return of past quotation. 
TERMS: Cash with order or C.O.D., please 
add 4s. for postage. 

C.O.D. orders will be charged 6s. 
Transformers fully guaranteed. (98 



LOOK I Nearly every type in stock now I ! 
NEW TELEVISION TUBES ! 

TWO YEAR FULL REPLACEMENT GUARANTEE 

SEETHE DIFFERENCE A NEW TUBE CAN MAKE TO YOUR VIEWING— 
LATEST SCREENING TECHNIQUES INCLUDING TINTED SCREENS ON 

19" & 23" TYPES 
Large stocks by Cathodeon &• other leading manufacturers so why buy 

ordinary rebuilds? Some Colour tubes available! 
12" £3 (not 110°) 14" to 16" (not 1 10°) £4 15 

1 7" £5 1 5 6 1 9" 1 901 & 1 9AH £7100 

Other 19" mono tubes— all £6 17 6. Carriage all 12/-. Most 21" mono 
tubes — £7 15 0, 23" mono tubes £9 10 0. Carriage 15/-. 
RIMBALDS, 19" £8 10 0; 23" £11 10 Carriage 

TWIN PANELS, 19" £9 17 6; 23" £12 10.0 20/- 

Bulk enquiries welcomed, special terms. 

PHILIP H. BEARMAN 

(Suppliers to H.M. Govt, etc.) 
6 POTTERS ROAD, NEW BARNET, 

Closed Thurs & Sat afternoons TEL. 449/1934 & 7873 



LOOK! BVA VALVES 

Vast selection available. Slightly 
dearer than no name valves but 
worth the extra cost! SAE for 
lists. 

For example:— PY81/800, EF80, 
PL84 8/3, PL81, PCF80, PCL82, 
4, 5 10/3, PCC89, PCL83, 
PCF86 12/3 PL36, 30 P19, 
30FLI 12/9 PFL200, U25, U26 
14/9 etc. Also introductory offer 
post paid, LATEST higher rating 
BY100 & 33 ohm res, 4/-. Also 
lists smoothing condensers etc. 



HERTS. 

(Robophone Service) 



' 



Here's money-making repair data for over 

1,000 Popular Models 

FROM 1969 RIGHT ^tf^tfHMHHHNB^ 
BACK T0 1965 ■ ^ # • rt 

»WflB^ T fi2^^ W "iS*i ^ 5 ist t2e Static ,o^- 

W aspects oiCgur^ ^ o«?^ c - ircaItSl ^° n sec . 

data FW* r „ mfl t e te coupon ™ B 

■ 69 LEADING MAKES COVERED 
A II you need from A Iba to Decca, from 
Ferguson to Sanyo — Full list shown overleaf 

TELEVISIONS including 148 pages on 

COLOUR TV 

• RADIOS • RADIOGRAMS 

• CAR RADIOS • RECORD PLAYERS 

• TAPE RECORDERS 



THE 

ONLY 
WORK 
OF ITS 
KIND 




Send no money- it's yours by 
post on a week's 

FREE TRIAL 

in maroon and gold III ■■ I M WM 

post this reply -paid coupon today—see overleaf 



clio & Television Servicing 

POPULAR MODELS FROM 1969 RIGHT BACK TO 1965 




Circuit Diagrf 




: . .■ .-:...-f M -j v. *■*, 

[3183 | EES-i 



^■■■■■•JiMtBiikaiiaBMMMai 



iponent Layout Diagrar 

«i.i ' r i- *> ■ 









ftj 






M VGi\iLElXL/E 



: 



. : 



Waveform 



Fast ago 

wi/l bo 

paid by 

Buckingham 

Press Ltd 



Servicing data for all thesemakes 
COLOUR TELEVISION (148 PAGES)- 
Baird, B.R.C., Bush, G.E.C., Murphy, 
Philips, Sobeil, Stella. 

MONO TV, RADIOS, RADIOGRAMS, 
CAR RADIOS, RECORD REPRODUCERS. 
TAPE RECORDERS- 

Aiwa Alba, Baird, Beogram, Beolit, Bush, 
Carousel, Cossor, Dansette, Decca, 
Defiant, Dynaport, Dynatron, Eddystone, 
Ekco, Elizabethan, Ever Ready. Ferguson, 
Ferranti, Fidelity, G.E.C., Grundig, 
H.M.V., Kolster-Brandes, Hitachi, Invicta, 
Mc Michael, Marconi phone, Masteradio, 
Motorola, Murphy, National, Newmatic, 
Pam, Perdio.Peto-Scott, Philips, 
Portadyne, Pye, Radiomobile, R.G.D., 
Regentone, Roberts' Radio, Sanyo, Sharp, 
Smith's Radiomobile, Sobeil, S.T.C., Sony, 
Standard, Stella, Stereosound, Teletron, 
Thorn, Trans Arena, Ultra, Van DerMolen 
World Radio. 

PlusrecentdevelopmentsirtRadio&TV 

Electronic Video- Recording and Reproduction— 
EVR system. Radio Receivers — Car radios. 
Stereo Multiplex reception. Capacitance Diode 
Tun ; ng, Colour Television Test Equipment — 
Crosshatch Generator, Deguassing Coil, E.H.T. 
Meter, Colour Bar Generator, Cathode Ray 
Oscilloscope. 

2,180 PAGES, 2,657 CIRCUITS, 
COMPONENT LAYOUT DIAGRAMS, 
PRINTED PANEL DIAGRAMS, 
TABLES AND WAVEFORM GRAPHS 
Complete panel on right, fold and post 



No postage 

stamp 

necessary if 

posted in 

Gt. Britain or 

Northern 

Ireland 



BUSINESS REPLY SERVICE 
Licence No. OF. 381/1 



BUCKINGHAM PRESS LTD., 

18-1 9 WARREN STREET, 

LONDON, W.1 



See it FRi:E 

Complete section below, 
fold a long A to A turning this 
section under. Then fold 
across at B and C and luck 
B into C so reply-paid 
section shows. Post today. 



1 


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=11 1 li \W\ 

|£ | f g*p»i 

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B O O >• O 

a. £ a "□ I— 



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OTick coupon above to examine 
Electrical Engineer's 
Reference 




Oven 2,000 I 
More than 2, 
Diagrams, Photo- 
graphs and Tables 



H> 



Motors, Wiring ami IiiMaitalifin. 
Applied Electronic!?. Automatic 
<-?0nrTOL€'OTuputerM.IjilN;st I.K.K. 
He§. requirement*. Kd neat ion, 
Tmimss, Cfty A Quftd«,etf. 

ff kej»t after free trio). J 2 f'-rfep„ 
then 9 monthly payments of 

1 4'.* 'paying: £6, (8s, (inc. post 
e:;id ppcktnjr) in oi/- Cosh in 
£ <Ja>K5 £6. 12$. (fVir. post or>^ 

p 3£ *ifl?). R V4/EERB/3926R 



Ill 



" NORTH STAR " 

LOOK NORTH FOR QUALITY AND 
RELIABILITY 

Fully rebuilt television tubes — all types 

Two years guarantee 

Look North — buy "North Star" 

9* 12". 14*. 17* £5. 0.0 

16", 19" £6. 0.0 

21 * £7. 2.6 

23" £7.10.0 

19" Panorama £9. 0.0 

23" Panorama £12. 0.0 

25" Panorama £16. 0.0 

'19 Twin Panel £10.10.0 

'23 ■ Twin Panel £1 3.1 0.0 

*N B Twin Panel tubes cannot be successfully 

rebuilt to our stringent standards — these types 

therefore are brand new 

Carriage and Insurance 10/- 

TERMS 

Cash or Cheque with order— state tube type 

required 

Two Years Guarantee 

"NORTH STAR" TUBE SUPPLY Co., 

P.O. Box 17. "HIGH RIGG". 
CARR BANK, OTLEY, YORKSHIRE 



L THE KING TELEBOOSTER '..] 


3Kb 


I 




' 


Ite^: 




FROM THIS - B» THI: - TQ THIS 



THE ORIGINAL VHF DUAL BAND TUNABLE 

PRE-AMPUFIER 

Still the best of its kind available. Latest low-noise transistor and 

printed circuit. Boosts Band I and II simultaneously without 

switching. Two amplifiers in one. Can produce good viewing 

out of almost nothing in fringe arcus. Ideal for DX work. 

Guaranteed gain: Minimum IBdB Band 1. l4dB Band 111 

Channels: Red spot, Band 1, 2 and 3. ail Band 3. 

Yd low spot. Band t. 3. 4 and 5. all Band 3. 

Power: Self-contained 9v PP4 battery. IfntA, 

Plastic case 32 x 3? x 2 in, brown, with cork base. 

Retail price. £3.15.6. complete with battery OR self-contained 

mains version, retail price £5.17,6, 

Specify channels, one Band I, one Hand lit. 

THE KING UHF TELEB00STER FOR BBC2 

Unique design, employing nuarier-wave cavity, resonator for 
"ability, printed circuit for reliability, with the very latest 
third generation low-noise transistor. 
Tunable. Covers channels - 1 -<>K. 
Plastic case 3 J x 3 j x 2 in. brown, with cork base. 
Retail price £4.17.6, complete with battery OR self-contained 
mains model, £6.15.0. 

Sole manufacturers : 

TRANSISTOR DEVICES LTD. 

BRIDGE HOUSE, NEWTON ABBOT, Devon 

Tel. 2457 Send for literature 



ENGINEERS TEST EQUIPMENT 
AND ACCESSORIES 

MULTIMETERS 

Complete range of high precision instruments. 

TRANSISTOR CHECKERS 

For use with PNP, NPN Transistors IF and 
RF Resistors, Diodes, Rectifiers. 

RESISTOR SUBSTITUTION BOX 

CAPACITANCE SUBSTITUTION BOX 

ADJUSTABLE AC DC CONVERTER 

TEST LEAD KITS, etc. 

We also stock large range of Microphones, 
Audio Units, Recording Tapes, Intercoms, 
Telephone Amplifiers, Car Radios, TV 
Spares etc. 

Send S.A.E for illustrated brochures and price list 

D. WEBB 

WHOLESALERS 

61-63 Clifton Street, Hull, E. Yorkshire 

Telephone 36016 



BBC2 KITS AND TEIEIVISION SPARES 

nHF'885. Modify yo\j net to BBC9 1056 to 1903 models covered. Select Ion i>I 

BMmfWtattr* conversion kits and tuners at reduced prices. Lirts available. 

SPECIAL OFFERS: Leading Brit, maker dual 4007628 trarialstd. I 

push button tuners £5-5-0, 405/625 transisld. IK panels £3-15-0 inel. circuita 

p.p. 4/6. 

EKCO/FERRANTI. 4 position push button valve type £5-10-0, p.p. 4,'8, 

SOBKLL/GEC dual 405/625 IF amp. sod o/p chassis lncl. circuit 43 '8. ULTRA 

19S0C to 2,'««4 625 IF amp. chassis and switch iticl. circuits 25/-, p.p. 4/6. 

UHF TUBERS. Tranststd., lncl. circuit, 60,"-, I'YK.KKCO valve type 55,'-. 

TV SIQSAL BOOSTER UNITS, Sens, gain all stations. FYE/LABGEAB trans'd. 

BBC1 TTA or UHF Battery -plug In", 7IK UHF Mains "pint in", 97/8. L'Hl' 

Masthead 85/-, Post tree 

FIREBALL TUBERS. Sew SB'S. Used/good condition 80K PUSH 

BUTTON; TUBERS. Per BibeU 280, BGIi 813, 619, BEG 17/18, 192. Usedgood 

oondttion 80'-, TURRET TUBERS. Sew PTE 13 eh. CTM range incremental 

l»oL valvar 85/-, CYLDOX C. SO,-. PP. 4/6. Many others available. Large 

select ion channel ooQs. 

LIBE OUTPUT TRAKSFS Popular types available, brand new exact replace- 

meiits fully guar. A selection which can be supplied, p.p. 4/8, C.O.D. 3/8. 

PHILIPS 17TG100 range, STELLA 1011/1026/ 70 ■ 

EKCO Ml to 381 (U25 tyoes) . . . . 42/8 

FERRANTI 1001 to 1011 i C2fl types) 

EKCO FERRABTI lT;'26 types) J0°/90* 
EKCO S4S to 377, FEREANTI 1021 ta 1088 
EKCO 880 60 894, FEERANTI 10B7 to 1008 
DECCA PM1. 2, 17 : DH3Q, DM4C (70°) . . 
FERG 808 to 436, 42. 8 1 SDD to 737 
FERG, BMV, MARCONI. ULTRA PHILOO 
3000, 2(100. 4600, 6603, 1100 ranges Jellypot oof- 
KB Q VP20. QV20/1, SO/1, BV10, 20. 30, SV2l> 46/- 

KS LFT50. 8«, 109, XV40, 60, SO 20/- 

H ARCONI, YTJ57, 1S9, 160, 161. 163, 164 . , 55/- 
GEC 302 to 320, 62 '8: lat^r models . . 7S/8 

HH VI 885/9, 1870/6, 42 8, 1E90 to 1924 . , 55,- 
PYE VT1T. C317. CTM17 CWM 
17, d UO Ui 510, 700 A/D, HI' IAL21O08).. 
PAH. niVICTA eqniv. lOPTfl to above Pye 
FETO BOOTT 1419 tc 1723 . 
PiOLCO 1P6Q'2161, 55/-, 1010 to 1060 
SOBELL TPS1S0. BC24, 54. 270, 370 ranges 
ULTRA 1770 to 2384, PILOT PT45Q to 850 
•■SCAN COILS, Frame O/P, frame/line oae. trans,, mains dropper, conlrobi, etc. 
SALVAGED COMPONENTS. Large selectiuu tor popnlsr models, clean service- 
able condition, turrets, transformers, tc. ENQUIRIES invited, quotations 
given C.O.D. despatch available. 

MANOR SUPPLIES 

64 GOLDERS MANOR DRIVE, LONDON, N.W.It 

Cillers: 589b HIGH ROAD (nr. Granville Road}, N. Finchlev, K.1E. 
HIL9118 (0X-44B91UJ. 



LOFT I nserts p.p. 2/-, 

42. 6 Alb- 855, 668 
688 Bush TV32, 36, 43 
70/ Bush TV53 to 69 
75- Conor 945 to 930 
78 6 i Ekco TP308 
65,- Emerson 790 range 
(Ferguson 203 to 248 



36- 



89 



Ferranti 14T4 to 17TB 20, 



82 8 
820 



Ferranti 14T6 to 21K6 33 
KB NF70. 0V30, PV40 
FVP20. gVIO, 80. 80 35,- 
KB RGD FeatherUght 50 - 
KB SGD WY05/627 35,- 
PETO SCOTT 733 Si/- 

PbJlcol961.iei9tol060 35- 
Philipi 17TG 100 range 35 - 
85 - Pye VT4 VT7 42 6 

58 6 RGD D17. 590 to 819 35 - 
H:> RECI 10-4,10-17, 192 35 - 
82/8, Ultra 1770. 1780 range 367- 



IV 




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